T cell regulation

ABSTRACT

Regulatory T cells (Treg) limit autoimmunity but can also attenuate the magnitude of anti-pathogen and anti-tumor immunity. Understanding the mechanism of Treg function and therapeutic manipulation of Treg in vivo requires identification of Treg selective receptors. A comparative analysis of gene expression arrays from antigen specific CD4+ T cells differentiating to either an effector/memory or a regulatory phenotype revealed Treg selective expression of LAG-3 (CD223), a CD4-related molecule that binds MHC class II. LAG-3 expression on CD4+ T cells correlates with the cells&#39; in vitro suppressor activity, and ectopic expression of LAG-3 on CD4 T cells confers suppressor activity on the T cells. Antibodies to LAG-3 inhibit suppression both in vitro and in vivo. LAG-3 marks regulatory T cell populations and contributes to their suppressor activity.

This application claims priority to provisional U.S. Application Ser.No. 60/451,039, filed Feb. 28, 2003, U.S. Application Ser. No.60/482,143, filed Jun. 24, 2003, and U.S. Application Ser. No.60/531,704, filed Dec. 22, 2003.

The United States government, National Institutes of Health, providedfunding (AI39480) for work that underlies the invention. Under the termsof that funding agreement, the United States government retains certainrights in the invention.

FIELD OF THE INVENTION

The invention relates to therapeutic and drug screening methods.

BACKGROUND OF THE INVENTION

A variety of diseases are characterized by the development ofprogressive immunosuppression in a patient. The presence of an impairedimmune response in patients with malignancies has been particularly welldocumented. Cancer patients and tumor-bearing mice have been shown tohave a variety of altered immune functions such as a decrease in delayedtype hypersensitivity, a decrease in lytic function and proliferativeresponse of lymphocytes. S. Broder et al., N. Engl. J. Ned., 299: 1281(1978); E. M. Hersh et al., N. Engl. J. Med., 273: 1006 (1965); Northand Burnauker, (1984). Many other diseases or interventions are alsocharacterized by the development of an impaired immune response. Forexample, progressive immunosuppression has been observed in patientswith acquired immunodeficiency syndrome (AIDS), sepsis, leprosy,cytomegalovirus infections, malaria, and the like, as well as withchemotherapy and radiotherapy. The mechanisms responsible for thedown-regulation of the immune response, however, remain to be fullyelucidated.

The immune response is a complex phenomenon. T lymphocytes (T-cells) arecritical in the development of all cell-mediated immune reactions.Helper T-cells control and modulate the development of immune responses.Cytotoxic T-cells (killer T-cells) are effector cells which play animportant role in immune reactions against intracellular parasites andviruses by means of lysing infected target cells. Cytotoxic T-cells havealso been implicated in protecting the body from developing cancersthrough an immune surveillance mechanism. Regulatory T cells block theinduction and/or activity of T helper cells. T-cells do not generallyrecognize free antigen, but recognize it on the surface of other cells.These other cells may be specialized antigen-presenting cells capable ofstimulating T cell division or may be virally-infected cells within thebody that become a target for cytotoxic T-cells.

Cytotoxic T-cells usually recognize antigen in association with class IMajor Histocompatibility Complex (MHC) products which are expressed onall nucleated cells. Helper T-cells, and most T-cells which proliferatein response to antigen in vitro, recognize antigen in association withclass II MHC products. Class II products are expressed mostly onantigen-presenting cells and on some lymphocytes. T-cells can be alsodivided into two major subpopulations on the basis of their cellmembrane glycoproteins as defined with monoclonal antibodies. The CD4+subset which expresses a 62 kD glycoprotein usually recognizes antigenin the context of class II antigens, whereas the CD8+ subset expresses a76 Kd glycoprotein and is restricted to recognizing antigen in thecontext of Class I MHC.

Augmentation of the immune response in immune compromised animals viainfusions of lymphokines, adoptive immunotherapy has met with variableand limited success. Methods are needed to improve this type oftreatment. For example, lymphocyte, blood and other cell infusions areprovided to immunodeficient patients in certain settings. However,accelerating and enhancing the reconstitution of a healthy T-cellpopulation could provide significant increased benefit and efficacy tosuch patients.

A number of conditions can result in deleterious T-cell activity. Forexample, T-cell mediated autoimmune and inflammatory diseases arecharacterized by deleterious T-cell activity in which T-cells whichrecognize self antigens proliferate and attack cells which express suchantigens. Other examples include the occurrence of graft rejectionmediated by host T-cells and graft vs. host disease.

Existing immunosuppressive therapies available to treat these conditionsinclude administration of immunosuppressive compounds such ascyclosporine A, FK506 and rapamycin. However, these therapies are notcompletely effective and are associated with significant adverse sideeffects such as nephrotoxicity, hepatotoxicity, hypertension, hirsutism,and neurotoxicity. Thus additional therapies which can more effectivelysuppress T-cell activity with fewer side effects are needed to treatthese conditions.

Lymphocyte homeostasis is a central biological process that is tightlyregulated. Tanchot, C. et al., Semin. Immunol. 9: 331-337 (1997);Marrack, P. et al., Nat. Immunol. 1: 107-111 (2000); C. D. Surh, C. D.and Sprent, J., Microbes. Infect. 4: 51-56 (2002); Jameson, S. C., Nat.Rev. Immunol. 2: 547-556 (2002). While the molecular control of thisprocess is poorly understood, molecules involved in mediating twosignaling pathways are thought to be essential. First, recognition ofself major histocompatibility (MHC) molecules is important inmaintaining naïve T cell homeostasis and memory T cell function. Takeda,S. et al., Immunity 5: 217-228 (1996); Tanchot, C. et al., Science276:2057-2062 (1997).

Furthermore, recent studies have demonstrated that T cell receptor (TCR)expression is required for the continued survival of naïve T cell.Polic, B. et al., Proc. Natl. Acad. Sci. 98: 8744-8749 (2001);Labrecque, N. et al., Immunity 15: 71-82 (2001). Second, cytokines thatsignal via the common gamma (γc) chain are critical for naïve T cellsurvival and homeostasis, particularly interleukin-7 (IL-7). Schluns, K.S. et al., Nat. Immunol. 1: 426-432 (2000); Tan, J. T. et al., Proc.Natl. Acad. Sci. 98: 8732-8737 (2001). All of these molecules positivelyregulate T cell homeostasis. In contrast, only CTLA-4 and TGF-β havebeen implicated in negatively regulating T cell homeostasis, althoughthis has jet to be confirmed by T cell transfer into lymphopenic hostsor analysis of neonatal expansion. Waterhouse, P. et al., Science 270:985-988 (1995); Tivol, E. A. et al., Immunity 3: 541-547 (1995); Lucas,P. J. et al., J. Exp. Med. 191: 1187-1196 (2000); Gorelik L. andFlavell, R. A., Immunity 12: 171-181 (2000).

LAG-3 is particularly interesting due to its close relationship withCD4. LAG-3 has a similar genomic organization to CD4 and resides at thesame chromosomal location. Bruniquel, D. et al., Immunogenetics 47:96-98 (1997). LAG-3 is expressed on activated CD4⁺ and CD8⁺ αβ Tlymphocytes and a subset of γδ T cells and NK cells. Baixeras, E. etal., J. Exp. Med. 176: 327-337 (1992); Triebel, F. et al., J. Exp. Med.171: 1393-1405 (1990); Huard, B. et al., Immunogenetics 39: 213-217(1994); Workman, C. J. et al., Eur. J. Immunol. 32: 2255-2263 (2002).Like CD4, LAG-3 binds to MHC class II molecules but with a much higheraffinity. Huard, B. et al., Immunogenetics 39: 213-217 (1994); Huard, B.et al., Eur. J. Immunol. 25: 2718-2721 (1995).

BRIEF SUMMARY OF THE INVENTION

In a first embodiment of the invention a method is provided for treatinga patient suffering from an autoimmune disease. Auto-immune T cellsisolated from the patient are transfected in vitro with an expressionconstruct comprising a coding sequence for CD223. The transfectedauto-immune T cells are then reinfused to the patient.

In a second embodiment of the invention a composition is provided. Thecomposition comprises antibodies which specifically bind to CD223 and ananti-cancer vaccine.

In another embodiment of the invention a kit is provided. The kitcomprises antibodies which specifically bind to CD223 and an anti-cancervaccine.

In a fourth embodiment of the invention an improved method is providedfor treating a cancer patient with an anti-cancer vaccine. An antibodywhich specifically binds to CD223 is administered to the cancer patient.An anti-cancer vaccine is also administered. The antibody increasesmagnitude of anti-cancer response of the cancer patient to theanti-cancer vaccine.

A fifth embodiment of the invention provides a method to overcomesuppression of an immune response to an anti-cancer vaccine. An antibodywhich specifically binds to CD223 is administered to a cancer patientwith regulatory T-cells which suppress an immune response to ananti-cancer vaccine. An anti-cancer vaccine is also administered to thepatient. The antibody increases the response of the cancer patient tothe anti-cancer vaccine.

In another embodiment of the invention a method is provided forincreasing number of T cells in a mammal. An inhibitory agent whichbinds to CD223 protein or CD223 mRNA is administered to the mammal. Theinhibitory agent inhibits activity or expression of CD223.

In yet another embodiment of the invention a method is provided fordecreasing number of T cells in a mammal. An expression construct whichencodes CD223 is administered to the mammal. CD223 is expressed from theexpression construct and concentration of CD223 in the mammal isincreased. The number of T cells in the mammal is decreased.

In still another embodiment of the invention a method is provided fordecreasing number of T cells in a mammal. A population of CD223+ T cellsis administered to the mammal. The concentration of CD223 in the mammalis increased and the number of T cells in the mammal is therebydecreased.

According to another aspect of the invention a polypeptide consisting of50 or less contiguous amino acid residues of CD223 is provided. Thepolypeptide comprises an amino acid sequence KIEELE as shown in SEQ IDNO: 5.

Another aspect of the invention is a fusion polypeptide which comprisesat least two segments. A first segment consists of 50 or less contiguousamino acid residues of CD223. The first segment comprises an amino acidsequence KIELLE as shown in SEQ ID NO: 5. The second segment comprisesan amino acid sequence which is not found in CD223 as shown in SEQ IDNO: 2 or 4.

In an additional embodiment a method is provided for testing substancesfor potential activity as a drug for treating cancer, autoimmunedisease, chronic infections, AIDS, or bone marrow transplantationrecipients. A test substance is contacted with a CD223 protein or CD223protein fragment comprising an amino acid sequence KIELLE as shown inSEQ ID NO: 5. Then one determines whether the test substance bound tothe CD223 protein or CD223 protein fragment. The test substance isidentified as a potential drug for treating cancer, autoimmune disease,chronic infections, AIDS, or bone marrow transplantation recipients ifthe test substance bound to the CD223 protein or CD223 protein fragment.

Another embodiment provided by the present invention is a method fortesting substances for potential activity as a drug for treating cancer,chronic infections, AIDS, or bone marrow transplantation recipients. Atest substance is contacted with a CD223 protein. CD223 activity isdetermined in the presence and absence of the test substance. A testsubstance is identified as a potential drug for treating cancer, chronicinfections, AIDS, or bone marrow transplantation recipients if the testsubstance inhibits the CD223 activity.

According to another aspect of the invention a method, is provided fortesting substances for potential activity as a drug for treatingautoimmune disease. A test substance is contacted with a CD223 protein.CD223 activity is determined in the presence and absence of the testsubstance. A test substance is identified as a potential drug fortreating autoimmune disease if the test substance increases the CD223activity.

Another embodiment of the invention is a method of testing substancesfor potential activity as a drug for treating cancer, chronicinfections, AIDS, or bone marrow transplantation recipients. A CD223+ Tcell is contacted with a test substance. CD223 expression is determinedin the cell in the presence and absence of the test substance. A testsubstance is identified as a potential drug for treating cancer, chronicinfections, AIDS, or bone marrow transplantation recipients if the testsubstance inhibits the CD223 expression in the T cell.

Yet another aspect of the invention is another method of testingsubstances for potential activity as a drug for treating autoimmunedisease. A test substance is contacted with a CD223+ T cell. CD223expression in the cell is determined in the presence and absence of thetest substance. A test substance is identified as a potential drug fortreating autoimmune disease if the test substance increases the CD223expression in the T cell.

Still another aspect of the invention is a method of isolating CD223+ Tcells or CD223− T cells. A mixed population of T cells is contacted withan antibody which specifically binds to CD223 according to SEQ ID NO: 2or 4. T cells which are bound to the antibody are separated from T cellswhich are not bound to the antibody. A population of CD223+ T cells anda population of CD223− T cells are thereby formed.

Another embodiment of the invention is an isolated soluble murine CD223protein comprising residues 1 to 431 and lacking residues 467 to 521.

Still another aspect of the invention is an isolated soluble human CD223protein comprising residues 1 to 440 and lacking residues 475 to 525.

Yet another aspect of the invention is a method for decreasing number ofT cells in a mammal. A soluble CD223 protein is administered to themammal. MHC class II-restricted/CD4+ T cell responses in the mammal arethereby modulated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A to 1E. HA specific CD4+ T cells become tolerant and developregulatory T cell activity upon adoptive transfer into C3-HAhightransgenic mice. (FIG. 1A) C3-HAhigh transgenic mice express high levelsof HA in various epithelial compartments, with the highest levelexpressed in pulmonary epithelia. C3-HAhigh recipients die 4-7 daysafter adoptive transfer of 2.5×106 HA-specific TCR transgenic (6.5) CD4+T cells due to pneumonitis associated with a transient effector phase ofactivation occurring prior to development of an anergic phenotype.Transfer of smaller numbers of 6.5 CD4+ T cells results in less severepulmonary pathology and the C3-HAhigh recipients survive the transfer.Residual 6.5 T cells become anergic as defined by their inability toproduce γ-interferon or proliferate to HA antigen in vitro. Micereceiving a sublethal dose of 6.5 T cells are protected from subsequentinfusion of 2.5×106 naïve 6.5 T cells. Thus, the initial tolerized Tcells develop Treg activity that suppresses lethal pneumonitis inducedby the second high dose of 6.5 T cells. (FIGS. 1B to 1E) Localization ofeffector/memory vs. suppressed T cells in C3-HAhigh mice. Naive 6.5 Tcells (Thy 1.1+/1.2−) were adoptively transferred into C3-HAhighrecipients (Thy 1.1−/1.2+), either in the absence or in the presence of6.5 anergic/Treg cells (Thy 1.1−/1.2+). Spleens and lungs were harvested3 days after adoptive transfer and Thy 1.1+ cells were stained byimmunohistochemistry. In the absence of Treg cells, T effector cells arescattered in the splenic follicles (FIG. 1B) and infiltrate thepulmonary vessels (FIG. 1C). In the presence of Treg cells, suppressedHA-specific 6.5 T cells become sequestered in the splenicperi-arteriolar lymphatic sheath (FIG. 1D) and fail to infiltrate thepulmonary vessels (FIG. 1E).

FIG. 2A-2C. LAG-3 is differentially expressed between anergic/Treg andeffector/memory CD4+ T cells and LAG-3 expression in anergic/Treg CD4+ Tcells is correlated with IL-10 expression. The differential expressionrevealed by gene chip analysis was confirmed by (FIG. 2A) quantitativereal-time RT-PCR. The differential expression of LAG-3 in earlier days(Day 2 to Day 4) extends to 30 days after adoptive transfer. (FIG. 2B)Cell surface LAG-3 protein levels were assessed by antibody staining.Splenocytes were harvested from C3-HAhigh, wild type B10.D2 miceimmunized with Vac-HA, or wt B10.D2 mice 5 days after i.v. injectionwith 6.5+/−Thy1.1+/− splenocytes, and prepared into a single cellsuspension. All samples were first incubated with whole rat IgG to blockFc receptors. Cells were stained with TCR specificanti-6.5-biotin+SA-APC, LAG-3-PE, or the corresponding isotype controls.Cells were double gated on the total lymphocyte population and 6.5positive lymphocytes. Isotype control-dashed line, Naïve cells—lightgray line, Effector/memory cells—dark gray line, Anergic/Tregcells—black line. (FIG. 2C) Analysis of multiple samples of anergic/Tregpopulations over many experiments confirms a direct correlation betweenLAG-3 level and IL-10 mRNA level.

FIG. 3A-3B. LAG-3 is expressed on induced Treg cells independently ofCD25 and is a marker of Treg function. (FIG. 3A) Anergic/Treg 6.5 CD4+ Tcells from C3-HAhigh recipient spleens 5 days after transfer werestained for LAG-3 and CD25 expression, compared to isotype controls.(FIG. 3B) Cells were sorted into 4 populations based on their surfaceLAG-3 and CD25 staining: LAG-3highCD25high, LAG-3highCD25low,LAG-3lowCD25high, and LAG-3lowCD25low. 1×105 of each of the differentsorted subsets of cells were added as suppressors in an in vitrosuppression assay with 1×104 naive 6.5 CD4+ as responders.LAG-3lowCD25low cells were least suppressive. LAG-3highCD25high,LAG-3highCD25low, and LAG-3lowCD25high are comparable in suppressiveactivity, with LAG-3highCD25high double positive cells exhibiting themost suppressive activity. This is the representative result of threereproducible experiments.

FIG. 4. Anti-LAG-3 antibodies block in vitro Treg activity. Monoclonalanti-LAG-3 antibody added to the in vitro suppression assay at aconcentration of 2 μg/ml, totally reverses the suppression of naïve 6.5CD4+ T cell proliferation in vitro by 6.5 CD4+ suppressors at asuppressor:responder ratio of 0.04:1.

FIG. 5A to 5C. Anti-LAG-3 antibody eliminates the in vivo suppression by6.5 CD4+ Treg cells by directly inhibiting Treg cells. (FIG. 5A)C3-HAhigh mice pretreated with 8,000 6.5 CD4+ T cells survivedsubsequent challenge with 2.5×106 6.5 CD4+ T cells given 4 days afterthe initial transfer establishment of Treg population (w/Protection).Without the sublethal pretreatment, the C3-HAhigh recipients died 4-6Days after lethal challenge (No Protection). Monoclonal anti-LAG-3antibody (200 μg) was given i.v. to the C3-HAhigh mice with the lethaldose of 6.5 T cells 4 days after they were pretreated with 8,000 6.5CD4+ T cells and another dose of 200 μg was given 2 days later.Anti-LAG-3 antibody treated mice could no longer tolerate the subsequentlethal challenge (Protection+aLAG-3). In contrast, treatment withisotype control antibody rat IgG1 could not eliminate the in vivosuppression (Protection+RatIgG1). (FIGS. 5B and 5C) Anti-LAG-3 mAb doesnot hyper-activate naive 6.5 CD4+ T cells in the absence of Treg.C3-HAhigh mice received either 2.5×10⁵ (sublethal dose; FIG. 5B) or8×10⁵ (partial lethality between 7 and 14 days after transfer; FIG. 5C)naive 6.5 CD4+ T cells in combination with anti-LAG-3 antibody, controlrat IgG1, or no antibody. No lethality was observed with the anti-LAG-3antibody infusions at the 2.5×10⁵ dose whereas lethality at 8×105 dosewas not affected by anti-LAG-3 antibody.

FIG. 6A to 6D. Role of LAG-3 in natural CD4+CD25+ T cells. (FIG. 6A)Natural CD4+CD25+ T cells have higher levels of LAG-3 mRNA expressioncompared to their CD4+CD25− counterpart. CD4+CD25+ and CD4+CD25− T cellswere purified from wild type BALB/c lymph nodes. CD4+CD25+ T cells, thepopulation documented to contain natural regulatory T cells, havesignificantly higher mRNA levels for CD25 and LAG-3, as well as forCTLA-4, GITR and Foxp3, as compared to their CD4+CD25− counterpart(Expression of each mRNA in the CD4+CD25− subset was normalized to avalue of 1). (FIG. 6B) LAG-3 surface staining is negative on CD4+CD25+natural regulatory T cells, as in their CD4+CD25− counterpart. However,intracellular staining for LAG-3 reveals a positive population inCD4+CD25+, but not in CD4+CD25− T cells. (FIG. 6C) Sorted CD4+ CD25+Tcells from BALB/c mouse lymph nodes were used as suppressors andCD4+CD25− T cells as responders in an in vitro suppression assay(suppressor:effector ratio of 0.04:1), with anti-CD3 antibodies (0.5μg/ml) as the T cell stimulus. Anti-LAG-3 antibodies at theconcentration of 50 μg/ml reverse the in vitro suppression of naturalCD4+CD25+ regulatory T cells whereas isotype control antibody does not.(FIG. 6D) After the suppressor assay in C, the CD4+CD25+ cells(distinguished from the effector cells by Thy1.2 marking) were stainedwith anti-LAG-3 or isotype control antibody.

FIG. 7. Ectopic expression of wild type but not mutant LAG-3 in CD25depleted 6.5 CD4+ T cells confers potent in vitro regulatory activity.6.5 CD4+ T cells were first depleted of any CD25+ “natural” Tregs andthen transduced with MSCV-based retroviral vectors encoding either GFPalone, GFP+ wild type LAG-3 or GFP+ a mutant LAG-3.Y73FΔCY that hasdiminished binding to MHC class II and cannot mediate downstreamsignaling. After a 10 day rest period, essentially no endogenous LAG-3staining was observed on GFP+6.5 CD4+ T cells transduced with theMSCV-GFP vector while high levels of LAG-3 staining were observed onGFP+6.5 cells transduced with the MSCV-LAG-3/GFP andMSCV-LAG-3.Y73FΔCY/GFP vectors. GFP+ cells from the MSCV-LAG-3/GFP andMSCV-LAG-3.Y73FΔCY/GFP transductions stained brightly with anti-LAG-3antibodies while MSCV-GFP transduced cells displayed virtually no LAG-3staining. GFP+ cells from each group were sorted and mixed at differentratios with APC, 5 μg/ml HA110-120 peptide and naïve 6.5 CD4+CD25− cellsin a proliferation assay.

FIG. 8 shows that ectopic expression of LAG-3 on a Phogin-specific Tcell clone confers protection from diabetes following co-transfer withsplenyocytes from NOD mice. 10⁷ pre-diabetic NOD splenocytes weretransferred alone (none) or in combination with Phogrin T-cell clone 4(obtained from John Hutton) cells transduced with vector (MIG), LAG-3,or a signaling-defective mutant, LAG-3□K, into NOD/SCID mice. NOD/SCIDmice (5/group) were monitored for diabetes.

DETAILED DESCRIPTION OF THE INVENTION

LAG-3 is a CD4-related, activation-induced cell surface molecule thatbinds to MHC class II with high affinity. We have found that aged LAG-3deficient mice have twice as many CD4⁺ and CD8⁺ T cells than wild typecontrols. LAG-3 deficient T cells show enhanced homeostatic expansion inlymphopenic hosts, which is dependent on LAG-3 ligation of MHC class IImolecules. This was abrogated by ectopic expression of wild type LAG-3but not by a signaling defective mutant. This deregulation of T cellhomeostasis results in the expansion of multiple cell types. Our datasuggest that LAG-3 negatively regulates CD4⁺ and CD8⁺ T cellhomeostasis, and present LAG-3 as a therapeutic target for acceleratingT cell engraftment following bone marrow transplantation.

CD223, also known as lymphocyte antigen gene-3 or LAG-3, is aCD4-related activation-induced cell surface protein that binds to MHCclass II molecules with high affinity. Baixeras, E. et al., J. Exp. Med.176: 327 (1992). See Triebel, F., “Lag-3(CD223)”, Protein Reviews oilthe Web (PROW) 3:15-18(2002) at the URL address: http file type, wwwhost server, domain name ncbi.nlm.gov, directory PROW, subdirectoryguide, document name 165481751_g.htm.; Triebel, F. et al., “LAG-3, anovel lymphocyte activation gene closely related to CD4”, J. Exp. Med.171: 1393-1405 (1990). A representative murine DNA and amino acidsequence for CD223 is set forth as SEQ ID NOS: 1 and 2, respectively.See also GenBank Accession Code X9113. A representative human DNA andamino acid sequence for CD223 is set forth as SEQ ID NOS: 3 and 4,respectively. See also GenBank Accession Number X51985. These sequencesare derived from single individuals. It is expected that allelicvariants exist in the population which differ at less than about 5% ofthe positions. Such allelic variants are included within the meaning ofCD223 of murine or human origin.

Regulatory T-cells are a subgroup of T-cells that function by inhibitingeffector T-cells. Regulatory T-cells are CD223⁺ and are typically alsoCD4⁺ CD25⁺. Regulatory T-cells play a central role in balancingautoimmune tolerance and immune responsiveness. Such cells can beisolated from CD223-cells using antibodies and separation techniquesknown in the art. These include but are not limited to immunoaffinitychromatography, FACS, immunoprecipitation, etc. The CD223⁺ cells can beadministered to autoimmune disease, allergy, or asthma patients. In thecase of an autoimmune disease patient the cells can be pre-activatedwith auto-antigen. CD223⁻ cells can be similarly transferred to cancerpatients, bacterial or vial infection patients, or AIDS patients.

A comparative analysis of gene expression arrays from antigen specificCD4+ T cells differentiating to either an effector/memory or aregulatory phenotype revealed Treg-specific expression of LAG-3, a CD4homologue that binds MHC class II. LAG-3high CD4+ T cells display invitro suppressor activity and antibodies to LAG-3 inhibit thesuppression both in vitro and in vivo. These findings identify LAG-3 asa Treg specific receptor or co-receptor modulating suppressor activity.Manipulation of Treg cells via LAG-3 can therefore be used to enhanceimmunotherapy of autoimmune diseases, cancer and infectious diseases aswell as enhance lymphocyte engraftment in settings of donor lymphocyteinfusion, bone marrow transplantation and adoptive T cell transfer.

CD223 is a regulatory T-cell specific cell surface molecule thatregulates the function of regulatory T-cells. The function of aregulatory T-cell may be enhanced by enhancing or increasing CD223activity, or by increasing the number of CD223+ cells in a T-cellpopulation. Enhancing the function of regulatory T-cells in an organismmay be used to limit the immune T-cell response in those circumstanceswhere such a response is undesirable, such as when a subject suffersfrom autoimmune disease. Conversely, the function of a regulatory T-cellmay be inhibited by inhibiting CD223 activity or by decreasing thenumber of CD223+ cells in a T-cell population. Inhibiting the functionof regulatory T-cells in an organism may be used to enhance the immuneT-cell response in those circumstances where such a response isdesirable, such as in a patient suffering from cancer, chronicinfection, or a bone marrow transplant recipient.

When treating a cancer patient with an inhibitory agent that binds toCD223 protein or mRNA, one may optionally co-administer an anti-tumorvaccine. Such vaccines may be directed to isolated antigens or to groupsof antigens or to whole tumor cells. It may be desirable to administerthe inhibitory agent with chemotherapeutic agents. Treatment withmultiple agents need not be done using a mixture of agents but may bedone using separate pharmaceutical preparations. The preparations neednot be delivered at the same exact time, but may be coordinated to bedelivered to a patient during the same period of treatment, i.e., withina week or a month or each other. Thus a composition comprising twoactive ingredients may be constituted in the body of the patient. Anysuitable anti-tumor treatment can be coordinated with the treatments ofthe present invention targeted to CD223. Similarly, if treating patientswith infections, other anti-infection agents can be coordinated with thetreatment of the present invention targeted to CD223. Such agents may besmall molecule drugs, vaccines, antibodies, etc.

The number of CD223⁺ cells in a T-cell population can be modified byusing an antibody or other agent that selectively binds to CD223. CD223⁺cells represent an enriched population of regulatory T-cells that can beintroduced back into the original source of the T-cells or into anothercompatible host to enhance regulatory T-cell function. Alternatively,the CD223⁻ cells represent a population of T-cells deficient inregulatory T-cell activity that can be reintroduced into the originalsource of the T-cells or another compatible host to inhibit or reduceregulatory T-cell function while retaining general T-cell activity.

Any desired means for either increasing or decreasing (modulating) CD223activity can be used in the methods of the invention. This includesdirectly modulating the function of CD223 protein, modulating CD223signal transduction, and modulating expression of CD223 in T-cells bymodulating either transcription or translation or both. Those meanswhich selectively modulate CD223 activity are preferred overnonselective modulators. Also, those inhibitory means which create atransient CD223 deficiency in a population of T-cells which then returnto normal levels of CD223 activity may be preferred for treating atemporary T-cell deficiency. The transiently deficient T-cells may beused to reconstitute a diminished T-cell population with T-cells thatwill be genetically normal with respect to CD223. Such a temporaryT-cell deficiency occurs, for example, in patients receiving a stem celltransfer following myoablation. Modulation of CD223 activity can beperformed on cells iz vitro or in whole animals, in vivo. Cells whichare treated in vitro can be administered to a patient, either theoriginal source of the cells or au unrelated individual.

To inhibit the function of CD223, CD223 antibodies or small moleculeinhibitors can be used. Antibodies or antibody fragments that are usefulfor this purpose will be those that can bind to CD223 and block itsability to function. Such antibodies may be polyclonal antibodies,monoclonal antibodies (see, e.g. Workman, C. J. et al., “Phenotypicanalysis of the murine CD4-related glycoprotein, CD223 (LAG-3)”, Eur. J.Immunol. 32:2255-2263 (2002)), chimeric antibodies, humanizedantibodies, single-chain antibodies, soluble MHC class II molecules,antibody fragments, etc.

Antibodies generated against CD223 polypeptides can be obtained bydirect injection of the CD223 polypeptides into an animal or byadministering CD223 polypeptides to an animal, preferably a nonhuman.The antibody so obtained will then bind the CD223 polypeptides itself.In this manner, even a sequence encoding only a fragment of the CD223polypeptide can be used to generate antibodies binding the whole nativeCD223 polypeptide.

For preparation of monoclonal antibodies, any technique which providesantibodies produced by continuous cell line cultures can be used.Examples include the hybridoma technique (Kohler and Milstein, 1975,Nature, 256:495-497), the trioma technique, the human B-cell hybridomatechnique (Kozbor et al., 1983, Immunology Today 4:72), and theEBV-hybridoma technique to produce human monoclonal antibodies (Cole, etal., 1985, in Monoclonal Antibodies and Cancer Therapy, Alan R. Liss,Inc., pp. 77-96).

Techniques described for the production of single chain antibodies (U.S.Pat. No. 4,946,778) can be readily used to produce single chainantibodies to CD223 polypeptides. Also, transgenic mice may be used toexpress humanized antibodies to immunogenic CD223 polypeptides.

To enhance or activate the function of CD223, any agent which increasesthe level of CD223 or the activity of existing CD223 in the T-cell maybe used. Such agents may be identified using the screening assaysdescribed below. Expression vectors encoding CD223 can also beadministered to increase the gene dosage. The expression vectors can beplasmid vectors or viral vectors, as are known in the art. Any vectorcan be chosen by the practitioner for particularly desirable properties.

Autoimmune disease which are amenable to treatments according to thepresent invention include autoimmune hemolytic anemia, autoimmunethrombocytopenia purpura, Goodpasture's syndrome, pemphigus vulgaris,acute rheumatic fever, mixed essential cryoglobulinemia, systemic lupuserythematosus, insulin-dependent diabetes mellitus, rheumatoidarthritis, Graves' disease, Hashimoto's thyroiditis, myasthenia gravis,and multiple sclerosis. Auto-immune T cells can be isolated fromautoimmune disease patients as is known in the art. These can betransfected with a coding sequence for CD223. Any desirable expressionvector can be used for expressing CD223. These include withoutlimitations plasmids and viral vectors. The expression regulatorysignals can be derived from CD223 itself or from other genes. Aftertransfection with CD223 expression construct the T cells can bereintroduced to the patient. Methods for infusing blood cells to apatient are well known in the art.

Compositions comprising a mixture of antibodies which specifically bindto CD223; and an anti-cancer vaccine can be made in vitro. Preferablythe composition is made under conditions which render it suitable foruse as a pharmaceutical composition. Pharmaceutical compositions may besterile and pyrogen-free. The components of the composition can also beadministered separately to a patient within a period of time such thatthey are both within the patient's body at the same time. Such atime-separated administration leads to formation of the mixture ofantibodies and vaccine within the patient's body. If the antibody andvaccine are to be administered in a time-separated fashion, they may besupplied together in a kit. Within the kit the components may beseparately packaged or contained. Other components such as excipients,carriers, other immune modulators or adjuvants, instructions foradministration of the antibody and the vaccine, and injection devicescan be supplied in the kit as well. Instructions can be in a written,video, or audio form, can be contained on paper, an electronic medium,or even as a reference to another source, such as a website or referencemanual.

Anti-CD223 antibodies of the invention can be used to increase themagnitude of anti-cancer response of the cancer patient to theanti-cancer vaccine. It can also be used to increase the number ofresponders in a population of cancer patients. Thus the antibodies canbe used to overcome immune suppression found in patients refractory toanti-cancer vaccines. The anti-cancer vaccines can be any that are knownin the art, including, but not limited to whole tumor cell vaccines,isolated tumor antigens or polypeptides comprising one or more epitopesof tumor antigens.

Expression of CD223 in T-cells can be modulated at the transcriptionalor translational level. Agents which are capable of such modulation canbe identified using the screening assays described below.

Translation of CD223 mRNA can be inhibited by using ribozymes, antisensemolecules, small interference RNA (siRNA; See Elbashir, S. M. et al.,“Duplexes of 21-nucleotide RNAs mediate RNA interference in culturedmammalian cells”, Nature 411:494-498 (2001)) or small moleculeinhibitors of this process which target CD223 mRNA. Antisense technologycan be used to control gene expression through triple-helix formation orantisense DNA or RNA, both of which methods are based on binding of apolynucleotide to DNA or RNA. For example, the 5′ coding portion of thepolynucleotide sequence, which codes for the mature polypeptides of thepresent invention, is used to design an antisense RNA oligonucleotide offrom about 10 to 40 base pairs in length. A DNA oligonucleotide isdesigned to be complementary to a region of the gene involved intranscription (triple helix—see Lee et al., Nucl. Acids Res., 6:3073(1979); Cooney et al, Science, 241:456 (1988); and Dervan et al.,Science, 251: 1360 (1991)), thereby preventing transcription and theproduction of CD223. The antisense RNA oligonucleotide hybridizes to themRNA in vivo and blocks translation of the mRNA molecule into the CD223polypeptide (Antisense—Okano, J. Neurochem., 56:560 (1991);Oligodeoxynucleotides as Antisense Inhibitors of Gene Expression, CRCPress, Boca Raton, Fla. (1988)). The oligonucleotides described abovecan also be delivered to cells by antisense expression constructs suchthat the antisense RNA or DNA may be expressed in vivo to inhibitproduction of CD223. Such constructs are well known in the art.

Antisense constructs, antisense oligonucleotides, RNA interferenceconstructs or siRNA duplex RNA molecules can be used to interfere withexpression of CD223. Typically at least 15, 17, 19, or 21 nucleotides ofthe complement of CD223 mRNA sequence are sufficient for an antisensemolecule. Typically at least 19, 21, 22, or 23 nucleotides of CD223 aresufficient for an RNA interference molecule. Preferably an RNAinterference molecule will have a 2 nucleotide 3′ overhang. If the RNAinterference molecule is expressed in a cell from a construct, forexample from a hairpin molecule or from an inverted repeat of thedesired CD223 sequence, then the endogenous cellular machinery willcreate the overhangs. siRNA molecules can be prepared by chemicalsynthesis, in vitro transcription, or digestion of long dsRNA by RnaseIII or Dicer. These can be introduced into cells by transfection,electroporation, or other methods known in the art. See Hannon, GJ,2002, RNA Interference, Nature 418: 244-251; Bernstein E et al., 2002,The rest is silence. RNA 7: 1509-1521; Hutvagner G et al., RNAi: Natureabhors a double-strand. Curr. Opin. Genetics & Development 12: 225-232;Brummelkamp, 2002, A system for stable expression of short interferingRNAs in mammalian cells. Science 296: 550-553; Lee N S, Dohjima T, BauerG, Li H, Li M-J, Ehsani A, Salvaterra P, and Rossi J. (2002). Expressionof small interfering RNAs targeted against HIV-1 rev transcripts inhuman cells. Nature Biotechnol. 20:500-505; Miyagishi M, and Taira K.(2002). U6-promoter-driven siRNAs with four uridine 3′ overhangsefficiently suppress targeted gene expression in mammalian cells. NatureBiotechnol. 20:497-500; Paddison P J, Caudy A A, Bernstein E, Hannon GJ, and Conklin D S. (2002). Short hairpin RNAs (shRNAs) inducesequence-specific silencing in mammalian cells. Genes & Dev. 16:948-958;Paul C P, Good P D, Winer I, and Engelke D R. (2002). Effectiveexpression of small interfering RNA in human cells. Nature Biotechnol.20:505-508; Sui G, Soohoo C, Affar E-B, Gay F, Shi Y, Forrester W C, andShi Y. (2002). A DNA vector-based RNAi technology to suppress geneexpression in mammalian cells. Proc. Natl. Acad. Sci. USA99(6):5515-5520; Yu J-Y, DeRuiter S L, and Turner D L. (2002). RNAinterference by expression of short-interfering RNAs and hairpin RNAs inmammalian cells. Proc. Natl. Acad. Sci. USA 99(9):6047-6052.

In addition to known modulators, additional modulators of CD223 activitythat are useful in the methods of the invention can be identified usingtwo-hybrid screens, conventional biochemical approaches, and cell-basedscreening techniques, such as screening candidate molecules for anability to bind to CD223 or screening for compounds which inhibit CD223activity in cell culture. As one example, the inventors have identifieda hen egg lysozyme (HEL), 48-62-specific,H-2A^(k-restricted murine CD)4⁺ T cell hybridoma 3A9 that does notexpress CD223, even after activation. Ectopic expression of wild type,but not signaling defective, CD223 significantly reduced the IL-2response of this T cell hybridoma to its specific peptide. This providesa simple in vitro assay system to screen for CD223 activity modulators.This latter method may identify agents that directly interact with andmodulate CD223, as well as agents that indirectly modulate CD223activity by affecting a step in the CD223 signal transduction pathway.

Cell-based assays employing cells which express CD223 can employ cellswhich are isolated from mammals and which naturally express CD223.Alternatively, cells which have been genetically engineered to expressCD223 can be used. Preferably the genetically engineered cells areT-cells.

Agents which modulate CD223 activity by modulating CD223 gene expressioncan be identified in cell based screening assays by measuring amounts ofCD223 protein in the cells in the presence and absence of candidateagents. CD223 protein can be detected and measured, for example, by flowcytometry using anti-CD223 specific monoclonal antibodies. CD223 mRNAcan also be detected and measured using techniques known in the art,including but not limited to Northern blot, RT-PCR, and arrayhybridization.

One particularly useful target sequence for identifying CD223 modulatorsis the amino acid motif KIEELE (SEQ ID NO: 5) in the CD223 cytoplasmicdomain which is essential for CD223 function in vitro and in vivo.Screening assays for agents which bind this motif will identifycandidate CD223 modulators whose activity as an inhibitor or activatorof CD223 can be further characterized through further testing, such asin cell based assays. This motif can be contained with in a polypeptidewhich consists of 50 or fewer contiguous amino acid residues of CD223.Alternatively, the motif can be contained within a fusion protein whichcomprises a portion of CD223 and all or a portion of a second(non-CD223) protein. The second protein may be a natural protein or canbe a synthetic polypeptide, for example containing a Histidine tag, orother useful polypeptide feature. Protein-protein binding assays arewell known in the art and any of a variety of techniques and formats canbe used.

CD223 can be post-translationally processed to yield a soluble form ofthe protein. The soluble form comprises at least amino acid residues 1to 431 of murine CD223, and at least amion acid residues 1 to 440 ofhuman CD223. The cytoplasmic tail is missing in each case. All or partof the transmembrane domain is missing as well. This soluble formmodulates responses of MHC class II-restricted/CD4+ T cells. Thus thesoluble form may be useful for administration to autoimmune diseasepatients, allergy patients, asthma patients, or cancer patients, forexample. Administration of the soluble form may be by any of convenientmeans, including infusion, topical, or intravenous administration.

In accordance with the teachings of the invention, CD223 inhibitors maybe administered to an organism to increase the number of T-cells in theorganism. This method may be useful for treating organisms sufferingfrom conditions resulting in a low T-cell population. Such conditionsinclude diseases resulting from immunodeficiency such as AIDS, as wellas disorders involving unwanted cellular invasion or growth, such asinvasion of the body by foreign microorganisms (bacteria or viruses) ortumor growth or cancer.

Such a T-cell deficiency is also an expected hazard for patientsreceiving a stem cell transfer following myoablation. The T-cells ofsuch patients are compromised and deliberately targeted for destructionso that they can be replaced with healthy donor T-cells. The process ofreconstituting a healthy T-cell population from a stem cell transfer cantake several months, during which time the patient is very susceptibleto opportunistic infections which can be life threatening. By inhibitingCD223 in the donor T-cells or using donor T-cells that have beenselected or engineered for a CD223 deficiency, T-cell division isenhanced and the process of T-cell reconstitution can be accelerated andthe period of T-cell deficiency can be reduced.

CD223 inhibitors may also be useful when administered in combinationwith conventional therapeutics to treat T-cell proliferation sensitivedisorders. For instance a tumor, which is a T-cell proliferationsensitive disorder, is conventionally treated with a chemotherapeuticagent which functions by killing rapidly dividing cells. The CD223inhibitors of the invention when administered in conjunction with achemotherapeutic agent enhance the tumoricidal effect of thechemotherapeutic agent by stimulating T-cell proliferation to enhancethe immunological rejection of the tumor cells.

In accordance with the teachings of the invention, CD223 activators orexpression enhancers may be administered to an organism to decrease thenumber of T-cells in the organism and thereby decrease deleteriousT-cell activity. This method may be useful for treating organismssuffering from conditions resulting in an abnormally high T-cellpopulation or deleterious T-cell activity, for example graft rejectionmediated by host T-cells, graft vs. host disease and T-cell mediatedautoimmune and inflammatory diseases such as rheumatoid arthritis, type1 diabetes, muscular sclerosis, etc. The methods of the invention may beapplied to any organism which contains T-cells that express. CD223. Thisincludes, but is not limited to, any mammal and particularly includeshumans and mice.

When methods of the invention are carried out in vivo, the effectiveamount of CD223 modulator used will vary with the particular modulatorbeing used, the particular condition being treated, the age and physicalcondition of the subject being treated, the severity of the condition,the duration of the treatment, the nature of the concurrent therapy (ifany), the specific route of administration and similar factors withinthe knowledge and expertise of the health practitioner. For example, aneffective amount can depend upon the degree to which an individual hasabnormally depressed levels of T cells.

When administered, the pharmaceutical preparations of the invention areapplied in pharmaceutically-acceptable amounts and inpharmaceutically-acceptably compositions. Such preparations mayroutinely contain salt, buffering agents, preservatives, compatiblecarriers, and optionally other therapeutic agents. When used inmedicine, the salts should be pharmaceutically acceptable, butnon-pharmaceutically acceptable salts may conveniently be used toprepare pharmaceutically-acceptable salts thereof and are not excludedfrom the scope of the invention. Such pharmacologically andpharmaceutically-acceptable salts include, but are not limited to, thoseprepared from the following acids: hydrochloric, hydrobromic, sulfuric,nitric, phosphoric, maleic, acetic, salicylic, citric, formic, malonic,succinic, and the like. Also, pharmaceutically-acceptable salts can beprepared as alkaline metal or alkaline earth salts, such as sodium,potassium or calcium salts.

CD223 modulators may be combined, optionally, with apharmaceutically-acceptable carrier. The term“pharmaceutically-acceptable carrier” as used herein means one or morecompatible solid or liquid filler, diluents or encapsulating substanceswhich are suitable for administration into a human. The term “carrier”denotes an organic or inorganic ingredient, natural or synthetic, withwhich the active ingredient is combined to facilitate the application.The components of the pharmaceutical compositions also are capable ofbeing co-mingled with the molecules of the present invention, and witheach other, in a manner such that there is no interaction which wouldsubstantially impair the desired pharmaceutical efficacy.

The pharmaceutical compositions may contain suitable buffering agents,including: acetic acid in a salt; citric acid in a salt; boric acid in asalt; and phosphoric acid in a salt. The pharmaceutical compositionsalso may contain, optionally, suitable preservatives, such as:benzalkonium chloride; chlorobutanol; parabens and thimerosal.

Compositions suitable for parenteral administration convenientlycomprise a sterile aqueous preparation of the anti-inflammatory agent,which is preferably isotonic with the blood of the recipient. Thisaqueous preparation may be formulated according to known methods usingsuitable dispersing or wetting agents and suspending agents. The sterileinjectable preparation also may be a sterile injectable solution orsuspension in a non-toxic parenterally-acceptable diluent or solvent,for example, as a solution in 1,3-butane diol. Among the acceptablevehicles and solvents that may be employed are water, Ringer's solution,and isotonic sodium chloride solution. In addition, sterile, fixed oilsare conventionally employed as a solvent or suspending medium. For thispurpose any bland fixed oil may be employed including synthetic mono- ordi-glycerides. In addition, fatty acids such as oleic acid may be usedin the preparation of injectables. Carrier formulation suitable fororal, subcutaneous, intravenous, intramuscular, etc. administrations canbe found in Remington's Pharmaceutical Sciences, Mack Publishing Co.,Easton, Pa.

A variety of administration routes are available. The particular modeselected will depend, of course, upon the particular drug selected, theseverity of the condition being treated and the dosage required fortherapeutic efficacy. The methods of the invention, generally speaking,may be practiced using any mode of administration that is medicallyacceptable, meaning any mode that produces effective levels of theactive compounds without causing clinically unacceptable adverseeffects. Such modes of administration include oral, rectal, topical,nasal, interdermal, or parenteral routes. The term “parenteral” includessubcutaneous, intravenous, intramuscular, or infusion. Intravenous orintramuscular routes are not particularly suitable for long-term therapyand prophylaxis. They could, however, be preferred in emergencysituations. Oral administration will be preferred because of theconvenience to the patient as well as the dosing schedule.

The pharmaceutical compositions may conveniently be presented in unitdosage form and may be prepared by any of the methods well-known in theart of pharmacy. All methods include the step of bringing the activeagent into association with a carrier which constitutes one or moreaccessory ingredients. In general, the compositions are prepared byuniformly and intimately bringing the active agent into association witha liquid carrier, a finely divided solid carrier, or both, and then, ifnecessary, shaping the product.

Compositions suitable for oral administration may be presented asdiscrete units, such as capsules, tablets, lozenges, each containing apredetermined amount of the active agent. Other compositions includesuspensions in aqueous liquids or non-aqueous liquids such as a syrup,elixir or an emulsion.

Other delivery systems can include time-release, delayed release orsustained release delivery systems. Such systems can avoid repeatedadministrations of the active agent, increasing convenience to thesubject and the physician. Many types of release delivery systems areavailable and known to those of ordinary skill in the art. They includepolymer base systems such as poly(lactide-glycolide), copolyoxalates,polycaprolactones, polyesteramides, polyorthoesters, polyhydroxybutyricacid, and polyanhydrides. Microcapsules of the foregoing polymerscontaining drugs are described in, for example, U.S. Pat. No. 5,075,109.Delivery systems also include non-polymer systems that are: lipidsincluding sterols such as cholesterol, cholesterol esters and fattyacids or neutral fats such as mono-di-and tri-glycerides; hydrogelrelease systems; sylastic systems; peptide based systems; wax coatings;compressed tablets using conventional binders and excipients; partiallyfused implants; and the like. Specific examples include, but are notlimited to: (a) erosional systems in which the anti-inflammatory agentis contained in a form within a matrix such as those described in U.S.Pat. Nos. 4,452,775, 4,667,014, 4,748,034 and 5,239,660 and (b)diffusional systems in which an active component permeates at acontrolled rate from a polymer such as described in U.S. Pat. Nos.3,832,253, and 3,854,480. In addition, pump-based hardware deliverysystems can be used, some of which are adapted for implantation.

Use of a long-term sustained release implant may be particularlysuitable for treatment of chronic conditions. Long-term release, areused herein, means that the implant is constructed and arranged todeliver therapeutic levels of the active ingredient for at least 30days, and preferably 60 days. Long-term sustained release implants arewell-known to those of ordinary skill in the art and include some of therelease systems described above.

While the invention has been described with respect to specific examplesincluding presently preferred modes of carrying out the invention, thoseskilled in the art will appreciate that there are numerous variationsand permutations of the above described systems and techniques that fallwithin the spirit and scope of the invention as set forth in theappended claims.

EXAMPLES Example 1 Negative Regulation of T Cell Homeostasis by LAG-3(CD223)

The following example shows that LAG-3 (CD223) negatively regulates CD4⁺and CD8⁺ T cell homeostasis, supporting its identification as a noveltherapeutic target for accelerating T cell engraftment following bonemarrow transplantation.

Wild type C57BL/6 mice have a constant number of αβ⁺ cells from 4 to 52weeks of age. As previously reported, young 4 week old LAG-3^(−/−) micehave normal T cell numbers. Miyazaki, T. et al., Science 272: 405-408(1996). In contrast, the number of αβ⁺ T cells in LAG-3^(−/−) micesteadily increases from 3 months of age to numbers ˜2-fold higher thanwild type mice. This difference is highly significant given the tighthomeostatic regulation of αβ⁺ T cell number evidenced by the very lowstandard deviation. Both CD4+ and CD8+ cells were increased inLAG-3^(−/−) mice but the CD4:CD8 ratio was unchanged. Similarly,LAG-3^(−/−) mice transgenic for the OT-II TCR (ovalbumin326-339-specific, H-2A^(b)-restricted) had an increased number CD4⁺ Vα2⁺T cells compared with wild type control OT-II transgenic mice, exceptthat these differences were evident at 5 weeks of age. Approximately 20%αβ⁺T cells and CD49b⁺ NK cells constitutively express LAG-3 in wild typemice (Workman, C. J. et al., Eur. J. Immunol. 32: 2255-2263 (2002)), andtheir numbers were also significantly increased in LAG-3^(−/−) mice.Surprisingly, several other cell types such B220⁺B cells, Gr-1⁺granulocytes and Mac-1⁺ macrophages, none of which express LAG-3, werealso increased in LAG-3^(−/−) compared with control mice. The increasedcell numbers observed in LAG-3^(−/−) mice was consistent with a −50%increase in the number of dividing BrdU⁺ cells in vivo. It is importantto note that the differences in cell number observed between LAG-3^(−/−)and wild type mice was highly consistent and reproducible. The absenceof LAG-3 did not appear to have any significant effect on the cellsurface phenotype of T cells from LAG-3^(−/−) mice. These data supportthe idea that LAG-3 regulates the number of T cells in mice, andindirectly affects leukocyte numbers in general.

To determine if LAG-3 influences the homeostatic expansion of T cells ina lymphopenic environment, purified T cells were adoptively transferredinto RAG^(−/−) mice, which lack T and B cells, and T cell number in thespleen determined 15 days post-transfer. There was a 2.8-fold increasein the number of LAG-3^(−/−) T cells compared with the wild typecontrol. Remarkably, only a small percentage of the wild-type T cellsexpressed LAG-3 despite the clear effect that the absence of LAG-3 hason T cell expansion. This infers that brief, transient expression ofLAG-3 may be sufficient for it to exert its effect on dividing cells.Increased expansion of CD4⁺ and CD8⁺ T cells was observed demonstratingthat both cell types were equally affected by the absence of LAG-3.Interestingly, there was also a two-fold increase in the number of αβ⁻host-derived cells in recipients of LAG-3^(−/−) versus LAG-3^(+/+) Tcells. This was consistent with the increased number of macrophages andgranulocytes observed in unmanipulated LAG-3^(−/−) mice. To ensure thatthe increased expansion of LAG-3^(−/−) T cells observed in RAG^(−/−)mice is independent of antigen specificity, we used purified T cellsfrom OVA [Ovalbumin 257-264-specific, H-2K^(b)-restricted; Hogquist, K.A. et al., Cell 76: 17-27 (1994)] and OT-II [Ovalbumin 326-339-specific,H-2A^(b)-restricted; Barnden, M. J. et al., Immunol. Cell Biol. 76:34-40 (1998)] transgenic mice. Wild-type CD4⁺ Vα2⁺ OT-II T cellsexpanded poorly in RAG^(−/−) mice, consistent with previous reportsindicating that these cells show little homeostatic expansion inlymphopenic hosts. Ernst, B. et al., Immunity 11: 173-181 (1999). Incontrast, this limitation did not apply to T cells from LAG-3^(−/−)OT-II transgenic mice, which expanded vigorously in lymphopenic hosts tonumbers that were 3.2-fold more that the wild-type T cells by 15 dayspost-transfer. Similarly, the number of LAG-3^(−/−) CD8⁺ Vα2⁺ OVAtransgenic T cells recovered from RAG-1^(−/−) mice was 4-fold higherthan wild-type control OVA T cells. Remarkably, this differencepersisted for at least a month post transfer. These data againdemonstrated that both CD4⁺ and CD8⁺ T cells are equally affected by theloss of LAG-3. To assess the importance of LAG-3 ligation by MHC classII molecules, LAG-3^(−/−) and wild type OVA transgenic T cells weretransferred into mice lacking both MHC class I and class II molecules(β2m^(−/−)×H-2Aβ^(b−/−)). The data clearly show that the enhancedexpansion of LAG-3^(−/−) T cells is abrogated in the absence of MHCclass II molecules, demonstrating the importance of this interaction.

LAG-3^(−/−) mice or adoptive recipients of LAG-3^(−/−) T cells haveincreased numbers of cells that are normally negative for LAG-3, such asB cells and macrophages. This supports the idea that an alteration inthe homeostatic control of T cells, due to the absence of LAG-3,directly alters the control of other leukocyte cell types. To test thisdirectly, B cells were co-transferred with either LAG-3^(−/−) orwild-type T cells into RAG^(−/−) mice. We also took advantage of thisapproach to assess the contrasting roles of MHC class II molecules inregulating T cells homeostasis. Previous studies have clearlydemonstrated that the homeostatic expansion and long-term survival ofCD4⁺ T cells requires periodic interaction with MHC class I molecules.Takeda, S. et al., Immunity 5: 217-228 (1996); Rooke, R., et al.,Immunity 7:123-134 (1997). In contrast, it is possible that theinteraction between LAG-3 and MHC class II molecules would have theopposite effect. As seen previously, there was a 3.0-fold increase inthe number of LAG-3^(−/−) T cells compared with the wild type controlwhen transferred with MHC class II^(−/−) B cells. However in thepresence of wild-type B cells, the difference between LAG-3^(−/−) andLAG-3^(+/+) T cell numbers increased to 4.9-fold. The increasedLAG-3^(−/−) T cell number is likely due to increased MHC: TCRinteraction, thus potentiating expansion. In contrast, the LAG-3^(+/+) Tcells would be subjected to both positive (via MHC: TCR interaction) andnegative (via MHC:LAG-3 interaction) homeostatic control which resultsin comparable expansion of wild-type T cells.

In the presence of wild-type T cells, the number of B cells recoveredfrom the spleen 7 days post-transfer was identical to mice receiving Bcells alone. In contrast, there was a 2.7-fold increase in the number ofB cells recovered from LAG-3^(−/−) T cell recipients, providing a directdemonstration that the increased B cell number was due to the‘deregulation’ of LAG-3^(−/−) T cells. Interestingly, there was anincrease in the number of MHC class II^(−/−) B cells in the presence ofwild-type T cells compared with mice receiving B cells alone. Thissupports the idea that the ‘local’ absence of LAG-3:MHC class IIinteraction can result in increased B cell expansion due to transientderegulation of wild-type T cells even though the recipient RAG^(−/−)mice have MHC class II⁺ macrophages and dendritic cells in the spleen.An alternate possibility is that ligation of MHC class II molecules byLAG-3 delivers a negative regulatory signal to B cells therebypreventing expansion. While this is plausible for B cells, it would notexplain the increased numbers of MHC class II cells, such asgranulocytes, in LAG-3^(−/−) mice. One possibility, which is currentlybeing investigated, is that the deregulated expansion of LAG-3^(−/−) Tcells results in their production of cytokines that induce the broadexpansion of many cell types.

The influence of LAG-3 expression on homeostatic expansion inlymphopenic mice is not limited to naïve T cells. Transfer ofantigen-experienced ‘memory’ OT-II T cells also resulted in asubstantially accelerated expansion of LAG-3^(−/−) T cells compared withthe wild-type control cells [7.2-fold]. It was important to verify thatLAG-3 was directly responsible for this ‘deregulated’ T cells expansionand not a closely linked gene that was disrupted by the originaltargeting strategy. Thus, LAG-3^(−/−) OT-II T cells were transduced withmurine stem cell virus (MSCV)-based retrovirus that contained eitherwild-type LAG-3 or a signaling defective mutant, LAG-3.ΔK^(M). Workman,C. J. et al., Eur. J. Immunol. 32: 2255-2263 (2002). The vector alsocontained an internal ribosomal entry site (IRES) and green fluorescentprotein (GFP) cassette to facilitate analysis of transduced cells.Persons, D. A. et al., Blood 90: 1777-1786 (1997). LAG-3^(−/−) andLAG-3^(+/+) OT-II T cells were also transduced with an ‘empty’vector/GFP alone control. Transduced cells were transferred intoRAG-1^(−/−) recipients and the number of OT-II T cells recovered 15-dayspost-transfer determined. As expected, the LAG-3^(−/−) GFP alone controlT cells expended more than the wild-type GFP cells [2.8-fold]. Ectopicexpression of LAG-3 reduced the number of OT-II T cells to a levelcomparable to the wild-type control, while expression of the LAG-3signaling defective mutant had no effect on homeostatic expansion. Thesedata demonstrate that LAG-3 is directly responsible for the effectsobserved.

Our data clearly show that LAG-3 negatively regulates homeostaticexpansion of T cells. They also support the idea that T cells maycontribute to the homeostasis of many cell types. Despite the cleareffect that the absence of LAG-3 had on T cells numbers in knockout miceand the expansion of T cells in lymphopenic mice, it was remarkable thatonly a very small percentage of T cells expressed LAG-3. Interestingly,ectopic expression of LAG-3 on all T cells did not have a greater effecton homeostatic expansion than the low-level, transient expression ofLAG-3 seen on wild-type cells. This suggests that the threshold forLAG-3 signaling may be very low, and that there may be other factorsthat limit the effect of LAG-3 signaling. Identifying the downstreamsignaling molecules(s) that interact with LAG-3 and determining themechanism by which LAG-3 regulates homeostatic expansion will clearly bean important focus of future research.

A surprising observation was the increased number of cells that do notexpress LAG-3, such as B cells and macrophages. Co-transfer experimentsclearly demonstrated that the absence of LAG-3 on T cells wasresponsible for the increase in other cells types observed. This couldbe due to a soluble or cell surface protein that is either induced byLAG-3 signaling that limits the number and/or expansion of other celltypes or produced due to the absence of negative regulation by LAG-3that limits the number and/or expansion of other cell types. The precisenature of this bystander expansion and its physiological role remain tobe determined.

Patients receiving bone marrow or mega dose stem cell transplants areparticularly susceptible to infections in the first 4-6 months due tothe slow rate of lymphocyte reconstitution. Our studies support the ideathat LAG-3 is a viable therapeutic target and that blocking LAG-3expression or function will accelerate T cell engraftment andsignificantly reduce this window of susceptibility.

Example 2 Materials and Methods

This example provides the experimental methods and materials for example1.

Mice: The following mice were used: LAG-3^(−/−) [obtained from Yueh-HsiuChen, Stanford University, Palo Alto, Calif., with permission fromChristophe Benoist and Diane Mathis, Joslin Diabetes Center, Boston,Mass.; Miyazaki, T. et al., Science 272: 405-408 (1996)]; C57BL/6J[Jackson Labs, Bar Harbor, Me.]; B6.PL-Thy1^(a)/Cy (Thy1.1 congenic)[Jackson Labs]; RAG-1^(−/−) [Jackson Labs, Bar Harbor, Me.; Mombaerts,P. et al., Cell 68: 869-877 (1992)]; MHC class II^(−/−) [provided byPeter Doherty, St. Jude Children's Research Hospital, Memphis, Term.;Grusby, M. J. et al., Science 253:1417-1420 (1991)]; MHC classI^(−/−)/II^(−/−) [Taconic, Germantown, N.Y.; Grusby, M. J. et al., Proc.Natl. Acad. Sci. U.S.A 90: 3913-3917 (1993)]; OT-II TCR transgenic mice[provided by Stephen Schoenberger, La Jolla Institute for Allergy andImmunology, La Jolla, Calif., with permission from William Heath, Walterand Eliza Hall Institute, Parkville, Victoria Australia; Barnden, M. J.et al., Immunol. Cell Biol. 76: 34-40 (1998)] and OT-I (OVA) TCRtransgenic mice [Jackson Labs; Hogquist, K. A. et al., Cell 76: 17-27(1994)]. Genome-wide microsatellite analysis demonstrated that 97% ofthe 88 genetic markers tested for the LAG-3^(−/−) mice were derived fromB6 mice (Charles River Laboratories, Troy, N.Y.). LAG-3^(−/−), MHC classII^(−/−), OT-I.LAG-3^(−/−) and OT-II.LAG-3^(−/−) colonies weremaintained in the St. Jude Animal Resource Center. All animalexperiments were performed in an AAALAC-accredited, SPF facilityfollowing national, state and institutional guidelines. Animal protocolswere approved by the St. Jude IACUC.

LAG-3 constructs and retroviral transduction: LAG-3 constructs wereproduced using recombinant PCR as described (Vignali, D. A. A. and K. M.Vignali, J. Immunol. 162: 1431-1439 (1999)). The LAG-3.WT andLAG-3.ΔK^(M) (LAG-3 with a deletion of the conserved KIEELE motif in thecytoplasmic tail) have been described (Workman, C. J. et al., J.Immunol. 169: 5392-5395 (2002)). LAG-3 constructs were cloned into amurine stem cell virus (MSCV)-based retroviral vector, which containedan internal ribosomal entry site (IRES) and green fluorescent protein(GFP), and retrovirus produced as described (Persons, D. A. et al.,Blood 90: 1777-1786 (1997); Persons, D. A. et al., Blood Cells Mol Dis.24: 167-182 (1998)). Retroviral producer cell lines were generated byrepeatedly transducing GPE+86 cells (7-10) times until a viral titer ofgreater then 10⁵/ml after 24 hr was obtained (Markowitz, D. et al., JVirol. 62: 1120-1124 (1988)).

Flow cytometry: Single cell suspensions were made from spleens and RBClysed with Gey's solution. Splenocytes were first stained with Fc Block,anti-CD16/CD32 (2.4G2) (BD PharMingen, San Diego, Calif.) for 10 min onice. The cells were then stained for the following cell surface markersusing various conjugated antibodies from BD PharMingen: αβ+ TCR(H-57-597), Vα2 (B20.1), γδ TCR (GL3), CD4 (RM4-4), CD8a (53-6.7),CD45R/B220 (RA3-6B2), CD11b/Mac1 (M1/70), Gr-1 (RB6-8C5), CD44 (IM7),CD25/IL2R (7D4), CD69 (H1.2F3) and CD244.2/NK cells (2B4). LAG-3expression was assessed with a biotinylated rat anti-LAG-3 mAb (C9B7W,IgG1 κ; Workman, C. J. et al., Eur. J. Immunol. 32: 2255-2263 (2002)) orthe same antibody obtained as a PE conjugate (BD PharMingen). The cellswere then analyzed by flow cytometry (Becton Dickinson, San Jose,Calif.).

Bromodeoxyuridine incorporation: At 5, 16, 28, and 52 weeks of age,LAG-3^(+/+), LAG-3^(−/−), OTII.LAG-3^(+/+) and OTII.LAG-3^(−/−) micewere given BrdU (Sigma, St. Louis, Mo.) in their drinking water for 8days (0.8 mg/ml). The mice were then sacrificed by CO₂ inhalation andthe spleens removed. Staining for BrdU incorporation was performed asdescribed (Flynn, K. J. et al., Proc. Natl. Acad. Sci. USA 96: 8597-8602(1999)). Briefly, the LAG-3^(−/−) and LAG-3^(+/+) splenocytes werestained for TCRαβ, CD4, CD8 and B220 expression. The OTII.LAG-3^(+/+)and OTII.LAG-3^(−/−) splenocytes were stained for Vα2 and CD4 expression(PharMingen). The cells were then fixed with 1.2 ml ice-cold 95% ethanolfor 30 min on ice. The cells were washed and permeabilized with PBS+1%paraformaldehyde+0.01% Tween 20 for 1 h at room temperature. The cellswere then washed and incubated with 50 KU of DNase (Sigma) in 0.15MNaCl+4.2 mM MgCl₂ pH 5.0 for 10 min at 37° C. BrdU was detected by theaddition of anti-BrdU-FITC (Becton Dickinson) for 30 min at RT and thenanalyzed by flow cytometry.

Adoptive transfer experiments: T cells and/or B cells from splenocyteswere either positively sorted by FACS or negatively sorted by magneticbead cell sorting (MACS). For FACS purifications, splenocytes werestained for TCR□□, CD4 and CD8 expression and sorted by positiveselection on a MoFlow (Cytomation, Ft. Collins, Colo.). For negativeMACS purification, splenocytes were stained with PE-coupled anti-B220,anti-Gr1, anti-Mac1, anti-TER119 (erythrocytes), anti-CD244.2 (NK cells)and anti-CD8 (for negative purification of OTII transgenic T cells). Thecells were then incubated with magnetic beads coupled with anti-PEantibody (Miltenyi Biotech, Auburn, Calif.) and then negatively sortedon an autoMACS (Miltenyi Biotech, Auburn, Calif.) to 90-95% purity. Insome experiments, T cells were labeled with carboxyfluorescein diacetatesuccinimidyl ester (CFSE). Cells were washed twice with PBS, resuspendedin PBS plus 0.1% BSA at 1×10⁷ cells/ml and incubated with 5 μM CFSE for10 min at 37° C. The cells were washed twice with PBS plus 0.1% BSA. Thepurified CFSE labeled or unlabeled T cells (5×10⁶ or 1×10⁷) and in somecases B cells (5×10⁶) were injected i.v. into RAG-1^(−/−) or Thy1.1⁺(B6.PL) mice.

Retroviral transduction of normal T cells: Spleens from OTII.LAG-3^(+/+)and OTII.LAG3^(−/−) mice were removed and single cell suspensions madeat 2.5×10⁶ cell/ml. The splenocytes were activated with OVA 326-339peptide [10 μM] in culture for two days. The activated splenocytes werethen incubated on a monolayer of GFP alone, LAG-3.WT/GFP orLAG-3.ΔK^(M)/GFP retroviral producer cells for 2 days in the presence ofpolybrene. The cells were allowed to rest for 10 days and then sortedfor Vα2⁺/CD4⁺/GFP⁺ expression by FACS. The cells were allowed to restfor two additional days and then 5×10⁶ cells were injected intoRAG^(−/−) mice via the tail vein. Fifteen days post-transfer, the micewere sacrificed by CO₂ inhalation and the spleens removed. Thesplenocytes were stained and analyzed by flow cytometry.

Example 3 Induced Treg Cells with Potent Regulatory Activity

In order to identify Treg specific molecules, we performed adifferential gene expression analysis of antigen-specific T cellsdifferentiating to either effector/memory cells in response to viralinfection or Treg cells upon encounter of cognate antigen as aself-antigen. This analysis revealed that the LAG-3 gene was selectivelyupregulated in Treg cells. The physiologic role of LAG-3, an MHC classII binding CD4 homologue, has not been clearly elucidated. Several invitro studies have suggested that LAG-3 may have a negative regulatoryfunction (Hannier et al., 1998; Huard et al., 1994; Workman et al.,2002a; Workman et al., 2002b). Here we show that membrane expression ofLAG-3 selectively marks Treg cells independently of CD25 and that LAG-3modulates both the in vitro and in vivo suppressive activity of Tregcells.

In order to study differences between T cell effector/memory andtolerance induction, we have utilized adoptive transfer of T cellreceptor (TCR) transgenic CD4+ T cells (clone 6.5) specific for a modelantigen—hemagglutinin (HA). In wild-type mice infected with recombinantHA-expressing vaccinia virus (Vac-HA), adoptively transferred HAspecific 6.5 CD4+ T cells differentiate into effector/memory cells uponencounter with HA. The effector/memory response is characterized by atypical expansion/contraction phase and the development of memorymarkers. When removed from the adoptively transferred animal, theseeffector/memory cells are hyper-responsive to HA in vitro relative tonaive 6.5 CD4+ T cells as assayed by antigen-specific proliferativeresponse and γ-interferon production. This memory response persists formonths after adoptive transfer. In contrast, adoptive transfer of 6.5CD4+ T cells into C3-HA transgenic mice, that express HA in multipleepithelial tissues, results in tolerance (Adler et al., 2000; Adler etal., 1998). Similar to the effector/memory response, there is a rapidexpansion/activation phase characterized by proliferation and expressionof effector cytokines, such as γ-interferon. However, after theactivation phase, the total HA-specific T cell pool contracts andresidual 6.5 cells fail to produce γ-interferon or proliferate in vitroupon antigen stimulation 4-7 days after adoptive transfer (Adler et al.,2000; Huang et al., 2003). The extinction of the capacity to producelymphokines such as IL-2 and γ-interferon and proliferate in response toantigen represents the standard operational definition of the anergicphenotype.

The intensity of the initial in vivo effector phase in C3-HA mice thatprecedes tolerance induction, is proportional to the number of 6.5 CD4+T cells adoptively transferred as well as the expression level of HAantigen in the recipient mice. Thus, C3-HA^(low) mice tolerate thetransfer of 2.5×10⁶ 6.5 CD4+ T cells quite well, but C3HA^(high) mice,which have 1000 fold higher HA expression than C3-HA^(low) mice, diewithin 4-7 days after transfer of 2.5×10⁶ 6.5 CD4+ T cells (FIG. 1A).The cause of death is lethal pulmonary vasculitis due to infiltration oftransgenic 6.5 CD4+ T cells in the lung, where HA expression is thehighest. Adoptive transfer of less than 2.5×10⁵ 6.5 CD4+ T cells intoC3-HA^(high) mice causes pulmonary vasculitis of less severity and therecipients survive (FIG. 1A) (Huang et al., 2003). Interestingly, 6.5CD4+ T cells transferred at a sublethal dose acquire a regulatoryphenotype as they are capable of protecting mice from death uponsubsequent infusion of what would be a lethal dose of 6.5 CD4+ T cellsin unprotected C3-HA^(high) mice. This in vivo regulatory function isextremely potent, since transfer of as few as 8,000 cells (0.3% of thelethal dose) will completely protect animals from death upon subsequentinfusion of 2.5×10⁶ naive 6.5 CD4+ T cells. Protection is observed asearly as 4 days after the initial transfer and remains active up to 6months (FIG. 1A). Depletion of CD4+ T cells, but not CD8+ T cells,before adoptive transfer totally eliminates the protective effect,thereby defining the Treg phenotype of anergized clonotypic 6.5 CD4+ Tcells.

Suppression of lethal pneumonitis is accompanied by an accumulation ofthe initial input (Treg) 6.5 T cells in the lungs and a drasticreduction in the number of infiltrating T effector cells from the secondinfusion. Instead of accumulating in the lungs, as occurs in the absenceof Treg cells, the T effector cells accumulate in the splenicperi-arteriolar lymphatic sheath (FIG. 1B). Further evidence that theanergic cells demonstrate Treg function comes from the finding that theyinhibit the activation of cytotoxic HA-specific CD8+ T cells in vivo(data not shown). Elimination of CD25+ T cells prior to the first(protective) adoptive transfer did not affect the development of Tregcells capable of protecting animals from a subsequent lethal challengeof 6.5 T cells. Therefore, it is likely that the Treg phenotype of theinitial input T cells was acquired after adoptive transfer as opposed tobeing a consequence of naturally occurring Treg cells among theadoptively transferred population. These findings are highly compatiblewith the published findings of Von Boehmer and colleagues, whodemonstrated that 6.5 CD4+ T cells rendered tolerant after transfer intotransgenic mice expressing HA in the B cell compartment in fact exhibitTreg function (Jooss et al., 2001).

Example 4 LAG-3 is Differentially Expressed on Induced Treg Cells

In order to identify genes associated with the anergic/Treg phenotype inour in vivo system, we performed Affymetrix chip analysis on purified6.5 CD4+ T cells either after adoptive transfer into non-transgenicrecipients followed by Vac-HA immunization to generate effector/memory Tcells or after transfer into C3-HA^(high) mice to generate anergic/Tregcells. Thy1.1(+)Thy1.2(−) congenic 6.5 T cells were purified fromThy1.1(−)Thy1.2(+) Vac-HA infected wild-type (effector/memory) orC3HA^(high) (anergic/Treg) recipients using a sequential isolationprocedure involving MACS Column depletion of CD8+ T cells, B cells andThy 1.2(+) T cells followed by flow cytometric sorting to >95% purity.This protocol avoids the use of TCR-specific or CD4 coreceptor specificantibodies that could potentially alter TCR or CD4 dependent geneexpression patterns.

RNA was isolated from naive 6.5 CD4+ T cells as the day 0 sample andisolated from 6.5 CD4+ T cells at days 2, 3 and 4 post-adoptive transferfor chip analysis. Genes that were differentially expressed betweenanergic/Treg populations and effector/memory populations were rankordered according to an algorithm that summed their differentialexpression from days 0-4. A surprisingly large number of genes wereselectively activated in anergic/Treg populations even at these earlytime points post adoptive transfer. Many of these genes represented ESTswith no known function. Among the genes that had been previouslyidentified, LAG-3 was among the most differentially expressed inanergic/Treg populations relative to effector/memory populations. Thisresult was subsequently validated by quantitative RT-PCR analysis with aLAG-3 primer-probe pair for various time points extended to 1 month postadoptive transfer. After a minimal initial increase in theeffector/memory cells, LAG-3 expression returns to baseline by 20 dayspost adoptive transfer. In striking contrast, LAG-3 expression increases20-50 fold over the first 5 days among anergic/Treg cell populations andremains high over the subsequent 4-week analysis (FIG. 2A). In contrast,levels of FoxP3, GITR and CTLA-4 showed modest increases (1.5-4 fold)that were similar in both effector/memory cells and the inducedanergic/Treg cells over the first 4-5 days (data not shown).

Cell surface expression of LAG-3 on populations of anergic/Treg 6.5 CD4+T cells relative to effector/memory 6.5 CD4+ T cells was then analyzedusing an anti-LAG-3 monoclonal antibody (Workman et al., 2002b) (FIG.2B). While there are very low levels of LAG-3 staining oneffector/memory cells, a significant proportion of anergic/Treg cellsfrom C3-HA^(high) transgenic mice display moderate to high levels ofLAG-3 staining, correlating with the gene expression results. As IL-10is commonly associated with differentiation and function of Treg (Mooreet al., 2001), we analyzed the endogenous levels of IL-10 mRNA and theircorrelation to the levels of LAG-3 mRNA in CD4+ T cell subsets fromC3-HAhigh transgenic mice (anergic/Treg 6.5 CD4+ T cells). Analysis ofmultiple samples of anergic/Treg populations over many experimentsrevealed correlation between LAG-3 mRNA level and IL-10 mRNA level witha correlation coefficient (12) of 0.87 (FIG. 2C).

Example 5 LAG-3 is Required for Maximal Treg Function

Cell surface expression of LAG-3 and CD25 on populations of anergic/Treg6.5 CD4+ T cells was analyzed coordinately using anti-LAG-3 andanti-CD25 monoclonal antibodies. Although similar proportions ofeffector/memory and anergic/Treg cells express CD25 (data not shown),LAG-3 and CD25 expression on anergic/Treg cells was not completelyconcordant (FIG. 3A). We therefore sorted the cells intoLAG-3^(high)CD25^(high), LAG-3^(high)CD25^(low), LAG-3^(low)CD25^(high),and LAG-3^(low)CD25^(low) populations and analyzed their regulatoryactivity in a standard in vitro suppression assay. In vitro suppressionof proliferative responses among naive 6.5 CD4+ cells showed that theLAG-3^(high)CD25^(high) population displayed the highest suppressiveactivity and the LAG-3^(low)CD25^(low) population had the lowest whilethe suppressive activity of the LAG-3^(high)CD25^(low) and theLAG-3^(low)CD25^(low) cells were comparable (FIG. 3B). These resultssuggest that, among induced Treg cells, the combination of LAG-3 andCD25 may mark Treg cells with the most suppressive activity.

To further evaluate the direct role of LAG-3 in regulating suppressionby induced Treg cells, we first determined whether anti-LAG-3 antibodiescould block the ability of LAG-3 expressing cells to suppress the invitro proliferative responses of naive HA-specific T cells. Anti-LAG-3antibodies at the concentration of 2 μg/ml inhibit suppression by Treg6.5 CD4+ T cells in the in vitro assay system (FIG. 4). Over the 2-dayassay period, anti-LAG-3 antibodies did not affect proliferativeresponses of 6.5 T cells stimulated in the absence of Treg, confirmingthat the effect of anti-LAG-3 antibodies was indeed on the Treg cellsand not the effector cells (data not shown). The ability of anti-LAG-3antibodies to block in vitro suppression by Treg cells demonstrates thatLAG-3 is not simply a Treg selective marker, but is a molecule thatmodulates Treg activity.

Example 6 LAG-3 is Required for Induced Treg Activity In Vivo

We next evaluated the role of LAG-3 in modulating in vivo Treg functionby determining whether administration of anti-LAG-3 antibodies couldblock suppression of lethal pneumonitis by Tregs in C3-HA^(high) mice.C3-HA^(high) mice were pretreated with 8,000 (sublethal dose) of 6.5CD4+ T cells followed by a subsequent dose of 2.5×10⁶ naive 6.5 CD4+ Tcells 4 days after the first transfer. As described above, Tregs havealready developed at this point. Anti-LAG-3 antibody (200 □g) wasadministered i.v. together with the subsequent challenge of 2.5×10⁶ 6.5cells and another 200 □g was given 2 days later. This antibody treatmenttotally eliminated the in vivo suppressive activity of the Treg cellsand the mice died in a time frame comparable to the C3-HA^(high) micelethally challenged without protective sublethal 6.5 pretreatment. Onthe contrary, mice with established Treg treated with isotype controlantibody (Rat IgG1) or no antibody survived subsequent challenge with2.5×10⁶ naive 6.5 T cells (FIG. 5A). While these results suggest thatthe anti-LAG-3 antibodies were blocking Treg activity in vivo, analternate formal possibility was that, rather than directly inhibitingTreg cells, the anti-LAG-3 antibodies hyper-activated the T cells in thechallenge population such that they overcame the inhibitory effects ofthe Tregs. To rule out this possibility, we asked whether in vivoadministration of anti-LAG-3 antibodies together with a dose of 6.5 Tcells just below the lethality threshold would cause lethality in theabsence of a preestablished Treg population. We therefore administered2.5×10⁵ 6.5 T cells (the maximal dose that will not cause lethality) or8.0×10⁵ 6.5 T cells (roughly 50% lethality between 7 and 14 days aftertransfer) into C3-HA^(high) mice together with anti-LAG-3 antibodies orisotype control. FIG. 5B demonstrates that the anti-LAG-3 treatment didnot render the 2.5×10⁵ 6.5 T cell dose lethal nor enhance the partiallethality of the 8.0×10⁵ 6.5 T cell dose. Therefore, the effect ofanti-LAG-3 antibodies in the experiment in FIG. 5A was to directlyinhibit Treg cells.

Example 7 LAG-3 is Expressed by Natural Treg Cells and is Required forSuppressor Activity

Taken together, these data confirm an important role for LAG-3 inmediating suppressor function of induced Treg. Given that therelationship between induced Treg and natural Treg remains unclear, itwas of interest to see whether LAG-3 was expressed selectively onCD4+CD25+T cells from wild type mice. LAG-3 mRNA (along with CTLA-4,FoxP3 and GITR mRNA) is indeed selectively expressed on CD4+CD25+cellscompared with CD4+CD25− cells (FIG. 6A). Despite this reproduciblefinding, we were unable to detect surface LAG-3 on either CD4+CD25+ orCD4+CD25− cells by antibody staining. However, antibody staining ofpermeabilized cells clearly indicated that 10-20% of CD4+CD25+ cellsexpressed intracellular stores of LAG-3. In contrast staining ofpermeabilized CD4+CD25− cells demonstrated absolutely noLAG-3+population (FIG. 6B). These findings suggested that at least somenatural Tregs possessed intracellular stores of LAG-3 that could berapidly recruited to the cell surface upon encounter with cognateantigen and subsequently mediate suppression. While natural Treg arecontained within the T cell population defined by CD4 and CD25, it isindeed possible that the actual Treg cells are those expressingintracellular LAG-3. To directly evaluate the role of LAG-3 in theregulatory function of natural Tregs, we asked whether anti-LAG-3antibodies could inhibit in vitro suppression mediated by purifiedCD4+CD25+ cells. FIG. 6C demonstrates that anti-LAG-3 antibodies indeedblock suppression mediated by purified CD4+CD25+ cells, suggesting thatLAG-3 plays a role in suppression mediated by natural as well as inducedTreg. Staining of the CD4+CD25+ cells at the end of the in vitrosuppression assay revealed that roughly 20% now express high levels ofLAG-3 on their surface, supporting the notion that the intracellularLAG-3 in mobilized to the surface under circumstances of TCR engagementand mediates regulatory activity (FIG. 6D).

Example 8 Ectopic Expression of LAG-3 Confers Regulatory Activity

The blocking experiments in FIGS. 5 and 6 suggest that LAG-3 is requiredfor maximal Treg function. To further validate this conclusion, weperformed a series of transduction experiments to determine if ectopicexpression of LAG-3 on T cells confers regulatory activity. For theseexperiments, 6.5 CD4+ T cells were first depleted of any CD25+“natural”Tregs and then transduced with MSCV-based retroviral vectors encodingeither GFP alone, GFP+ wild type LAG-3 or GFP+ a mutant LAG-3.Y73FΔCYthat has substantially reduced affinity for MHC class II and cannotmediate downstream signaling (Workman et al., 2002a). After a 10 dayrest period, essentially no endogenous LAG-3 staining was observed onGFP+ 6.5 CD4+ T cells transduced with the MSCV-GFP vector while highlevels of LAG-3 staining were observed on GFP+ 6.5 cells transduced withthe MSCV-LAG-3/GFP and MSCV-LAG-3.Y73FΔCY/GFP vectors. GFP+ cells fromeach group were sorted and mixed at different ratios with APC, HA¹¹⁰⁻¹²⁰peptide and naïve 6.5 CD4+CD25− cells in a proliferation assay. As shownin FIG. 7, 6.5 cells expressing wild type LAG-3 potently suppressedproliferation of naïve 6.5 cells while no suppression was observed withcontrol GFP transduced 6.5 cells or 6.5 cells expressing thenon-functional LAG-3.Y73FΔCY mutant. Total proliferation was in factsomewhat increased in these two latter groups, since GFP andLAG-3.Y73FΔCY transduced 6.5 cells themselves proliferate in addition tothe naïve 6.5 cells in the assay. Indeed, wild type LAG-3 transduced Tcells themselves demonstrated a significant reduction in proliferativeresponses apart from inhibiting proliferation of the non-transduced 6.5cells. These results provide direct evidence confirming the functionalrole of LAG-3 in suppression. Interestingly, LAG-3 transduction did notinduce other genes associated with Tregs, including Foxp3, CD25, CD103and GITR (data not shown). This result, together with the lack ofsignificant differential expression of these genes between 6.5 T cellsdifferentiating to effector/memory vs anergic/Treg phenotypes, suggeststhat LAG-3 may mediate a distinct pathway of regulatory T cell functionindependent of the Foxp3 pathway.

Example 9 Discussion

These findings identify LAG-3 as a cell surface molecule selectivelyupregulated on Treg cells that may be directly involved in mediatingTreg function. Given the many systems in which both natural and inducedTreg activity has been defined, it remains to be determined whetherLAG-3 is a “universal” Treg marker or selectively marks only certainTreg subsets. Our results suggest that in addition to induced CD4+ Tregcells, LAG-3 plays at least some role in mediating suppression bynatural CD4+CD25+Treg cells. Furthermore, other experimental datademonstrate a role for LAG-3 in the regulation of homeostatic lymphocyteexpansion by natural Treg (Workman and Vignali, accompanying paper). Thefinding that LAG-3 expression is significantly greater among CD4+CD25+Tcells from wildtype mice suggests that it may play a role in thefunction of natural, as well as induced, Tregs. As suggested by theexperiments in FIG. 3, the combination of LAG-3 and CD25 may define Tregsubsets with the most potent suppressive activity. We do not proposethat LAG-3 is a “lineage marker” for Treg as it is expressed at variablelevels that correlate with the magnitude of regulatory activity in invitro assays. In fact, it is not clear that Treg represent a stablelineage or differentiation state capable of promoting tolerance in anon-cell autonomous fashion (von Boehmer, 2003). Different mechanismshave been identified for Treg function in different systems (reviewed inShevach, 2002). LAG-3^(high) cells produce increased amounts of IL-10and display enhanced in vitro suppressor activity but the role of IL-10in mediating suppressive function in our system remains to bedetermined. Antibodies to LAG-3 inhibit the suppressor activity of Tregcells both in vitro and in vivo. We therefore propose that LAG-3 is aTreg specific receptor or coreceptor that modulates the suppressoractivity of this T cell subset.

A number of studies have suggested a cell autonomous inhibitory role forLAG-3 (Huard et al., 1994; Workman et al., 2002b), although initialstudies with LAG-3 KO mice failed to uncover any evidence for overtautoimmunity or hyperimmunity (Miyazaki et al., 1996). Given ourproposed role for LAG-3 in Treg function, it might be expected thatLAG-3 knockout mice would display multi-system autoimmunity (i.e.,similar to Foxp3 knockout or scurfy mice), which has not been reportedin these mice. However, there are clearly regulatory T cell defectsdisplayed by LAG-3 knockout mice, such as a defect in regulatingcellular homeostasis (Workman and Vignali, accompanying paper). We arein the process of reexamining older LAG-3 knockout mice for more subtleevidence of late-onset autoimmunity, as was observed in PD-1 knockoutmice (Nishimura et al., 1999; Nishimura et al., 2001). It is alsoconceivable that other regulatory mechanisms might have been enhanced inthese mice to compensate for the loss of LAG-3 expression.

Because it is expressed at higher levels on Treg cells, LAG-3 providesan excellent potential target for selective manipulation of Tregactivity to treat both cancer and autoimmune disease. CD25, the “goldstandard” Treg marker, is induced at high levels in activated cells, asit is a critical component of the IL-2 receptor complex. The apparentreason that CD4+ CD25+cells are enriched in Treg activity is not becauseCD25 is specific to Treg function, but rather because Treg cells arechronically stimulated by continuous encounter with self-antigen in theperiphery. More recently, the TNF receptor super-family member 18molecule (also called GITR) was demonstrated to be up-regulated on Tregcells. Furthermore, antibodies to GITR have been reported to inhibitTreg activity both in vivo and in vitro. However, GITR is equivalentlyup-regulated on activated T cells and therefore is apparently no moreselective as a marker for Treg cells than is CD25 (McHugh et al., 2002;Shimizu et al., 2002). Moreover, there are numerous reports thatCD4+CD25− cell populations can suppress certain immune functions(Annacker et al., 2001; Apostolou et al., 2002; Curotto de Lafaille etal., 2001; Graca et al., 2002; Shimizu and Moriizumi, 2003; Stephens andMason, 2000). Nonetheless, the finding that CD25^(high)LAG-3^(high)cells exhibit the greatest suppressive activity suggests that antibodiesagainst both of these cell surface molecules may be used coordinately tomanipulate Treg activity.

Our data show that LAG-3 is required for the maximal suppressiveactivity of both natural and induced Treg cells. However, is itsufficient? Thus far, the only molecule shown to confer regulatoryactivity on activated T cells is Foxp3 (Fontenot et al., 2003; Hori etal., 2003). Importantly we have shown here that ectopic expression ofLAG-3, but not a functionally defective mutant, on CD4+ T cells can alsoconfer regulatory activity.

Another key question is whether Treg cells suppress the reactivity ofCD4+ and CD8+ effector cells through direct T-T interactions or throughDC intermediaries. The identification of Treg selective and functionalexpression of LAG-3, a MHC class II binding molecule, should provide anew handle on dissecting mechanisms and manipulating Treg function fordiseases in which these cells play an important role.

Example 10 Experimental Procedures

Transgenic Mice

The C3-HA transgenic mice have been previously described (Adler et al.,2000; Adler et al., 1998). In short, the hemagglutinin (HA) gene derivedfrom the influenza virus A/PR/8134 (Mount Sinai strain) has been placedunder the control of the rat C3(1) promoter. Two founder lines wereestablished in the B10.D2 genetic background. These two founder lines,C3-HA^(high) and C3-HA^(low), which contain 30-50 and 3 transgene copiesrespectively, express the C3-HA hybrid mRNA in the same set ofnon-lymphoid tissues including the lung and prostate. While thedifference in total HA protein expression between C3-HA^(high) andC3-HA^(low) was not directly measured, in the lung and prostate, wherethe expression levels are highest, the difference is roughly 1000-foldas shown by bioassay of tissue extract induced hybridoma cytokinerelease.

The TCR transgenic mouse line 6.5, that expresses a TCR recognizing anI-E^(d)-restricted HA epitope (¹¹⁰SFERFEIFPKE¹²⁰; SEQ ID NO: 7)(generously provided by Dr. Harald von Boehmer, Harvard University,Boston, Mass.), was back-crossed 9 generations onto the B10.D2 geneticbackground. The other TCR transgenic mouse line Clone-4, that expressesa TCR recognizing a K^(d)-restricted HA epitope (⁵¹⁸IYSTVASSL⁵²⁶; SEQ IDNO: 8) (generously provided by Dr. Linda Sherman, Scripps ResearchInstitute, La Jolla, Calif.), was also back-crossed more than 9generations onto the Thy 1.1/1.1 B10.D2 genetic background. Because noclonotypic antibody is available for Clone-4 TCR, Thy 1.1 was used as asurrogate marker. Following adoptive transfer into Thy1.2/1.2recipients, we can assume that all the Thy 1.1⁺ CD8⁺ T cells express theHA-specific clonotypic TCR as nearly all of the mature CD8⁺ T cells inthe Clone-4 mice directly recognize the K^(d)-restricted HA epitope(Morgan et al., 1996).

Transgenic mice used for experiments were between the age of 8 to 24weeks. All experiments involving the use of mice were performed inaccordance with protocols approved by the Animal Care and Use Committeeof the Johns Hopkins University School of Medicine.

Adoptive Transfer

Clonotypic CD4⁺ or CD8⁺ T cells were prepared from pooled spleens andlymph nodes of 6.5 or Clone-4 transgenic mice. Clonotypic percentage wasdetermined by flow cytometry analysis. The activation marker CD44 wasanalyzed to ensure that these clonotypic cells were not activated indonor mice and were naive in phenotype. After washing 3 times with HBSS,an appropriate number of cells were resuspended in 0.2 ml of HBSS fori.v. injection through the tail vein.

Immunohistochemistry

Tissues were harvested from mice three days after adoptive transfer.Tissue was fixed in ImmunoHistoFix (A Phase sprl, Belgium) for 3 days at4° C. and then embedded in ImmunoHistoWax (A Phase sprl, Belgium).Serial sections were stained using biotin-labeled anti-Thy1.1 mAb(PharMingen, San Diego, Calif.). The Vectastain ABC kit (Vector,Burlingame, Calif.) and NovaRed (Vector) were used for development.Sections were counterstained with hematoxylin QS (Vector). Sections wereanalyzed using a Nikon Eclipse E800. Final image processing wasperformed using Adobe PhotoShop (Mountain View, Calif.).

Enrichment and Purification of In Vivo Primed 6.5 CD4+ T Cells

With either effector/memory or tolerance induction in vivo afteradoptive transfer, the clonotypic percentage of 6.5 CD4+ T cells in thespleens of recipient mice is only 0.2%˜5%. Deliberate enrichment andpurification is mandatory to obtain enough clonotypic CD4+ T cells forfurther studies, such as for Affymetrix gene chip analysis. Donor 6.5 Tcells were crossed onto a Thy1.1(+)Thy1.2(−) background which allowedfor a two step enrichment and purification procedure after adoptivetransfer into Thy1.1(−)/Thy1.2(+) recipients. 6.5 CD4+ T cells werefirst enriched by using biotinylated anti-CD8 (Ly-2, 53-6.7), anti-B220(RA3-6B2), and anti-Thy1.2 (30-H12) antibodies (all purchased from BDBiosciences PharMingen, San Diego, Calif.) and MACS streptavidinmicrobeads and MACS LS separation column (Miltenyi Biotech, Auburn,Calif.) to deplete CD8+ T cells, B cells and the recipient T cells (Thy1.2+). Since CD4+ T cells and CD8+ T cells are the only populationsbearing Thy1.1, and because CD8+ T cells had been depleted duringenrichment, sorting for Thy1.1(+) cells using FACSVantage SE cell sorter(BD Biosciences) resulted in highly purified 6.5 CD4+ T cells (95%).This technique avoids the use of TCR-specific or CD4 coreceptor specificantibodies that could potentially alter TCR or CD4 dependent geneexpression patterns.

Gene Chip Analysis

Sorted cells were sheared with Qiashredder columns (Qiagen, ValenciaCalif.), followed by total RNA isolation using the RNeasy kit (Qiagen).cDNA was synthesized using the Superscript Choice kit (Gibco/BRL) and anHPLC purified T7-DT primer (Proligo, Boulder, Colo.). Biotinylated cRNAprobe was prepared using the ENZO BioArray RNA transcript kit(Affymetrix, Santa Clara, Calif.). Murine gene chips U174A, B and C werehybridized and analyzed according to standard Affymetrix protocols.

Ranking the Differential Expression of Genes in CD4⁺ T Cells BetweenAnergy/Treg Induction and Effector/Memory Induction.

mRNA prepared from purified naïve 6.5 clonotypic CD4⁺ T cells andanergic/Treg and effector/memory 6.5 clonotypic CD4⁺ T cells on variousdays after adoptive transfer was analyzed by Affymetrix gene chips. Thedifferential expression of genes between anergy/Treg induction andeffector/memory induction was ranked by “distance”. The distance wasdefined as the sum of the absolute differences of expression betweenanergic T cells and effector/memory T cells on day 2 (|d1|), day 3(|d2|), and day 4 (|d3|) after adoptive transfer, divided by the valueof naïve CD4⁺ T cells (n) for normalization.

Antibodies and Staining

The following antibodies were used. Anti-LAG-3 (C9B7W, from PharMingen)(Workman et al., 2002b) either purified or PE conjugated; anti-CD25(7D4, from PharMingen) either purified or FITC conjugated; and anti-GITR(polyclonal antibody purchased from R&D Systems). For cell surfacestaining for LAG-3 and CD25, splenocytes from 6.5+/−Thy1.1+/− transgenicmice were isolated and enriched for CD4+ using a CD4+ negative selectionisolation kit (Miltenyi Biotec). Approximately 2.5×10⁶ clonotypic 6.5cells, as determined by flow cytometry (16% of total CD4+ cells) wereresuspended in HBSS and injected via tail vein into 137 (C3-HA high) orwild type B10.D2. One group of B10.D2 mice was treated with 5×10⁶Vac-HA, while the other group was left untreated for naïve control.Splenocytes and inguinal and axillary lymph nodes were harvested fivedays later and prepared into a single cell suspension. RBCs were lysedwith ACK lysis buffer. Cells were immediately blocked with 5 ug wholerat IgG (Sigma) for 15 minutes before staining with anti-6.5TCR-biotin+SA-APC, LAG-3-PE, and CD25-FITC, or the corresponding isotypecontrols. All staining reagents except anti-6.5-biotin were purchasedfrom Pharmingen (San Diego, Calif.). After short incubation, sampleswere washed once in PBS+1% FBS solution and read on a FACScaliburmachine (BD, San Jose, Calif.).

In Vitro Suppression Assay for Induced 6.5 Regulatory T Cells

1×10⁴ purified naive 6.5 CD4+ T cells (Responders) and 1×10⁵ 3000-radirradiated syngeneic B10.D2 splenocytes (Antigen Presenting Cells) weremixed with different numbers of suppressor 6.5 CD4+ T cells andincubated in round bottom 96-well tissue culture plates with 10 μg/ml ofHA class II (¹¹⁰SFERFEIFPKE¹²⁰; SEQ NO: 7) peptide in 200 μl of CTLmedia. Forty-eight to 72 hours later, cultures were pulsed with 1 μCi³H-thymidine and incubated an additional 16 hours before harvest with aPackard Micromate cell harvester. Determination of the amount ofincorporated radioactive counts was performed with a Packard Matrix 96direct beta counter (Packard Biosciences, Meriden, Conn.).

In Vitro Suppression Assay for Natural Regulatory T Cells

Wild type BALB/c mice were used for out natural Treg assays. 5×10⁴ flowcytometry sorted CD4+CD25− T cells (Responders) and 5×10⁴ 3000-radirradiated BALB/c splenocytes (Antigen Presenting Cells) were mixed withdifferent numbers of flow cytometry sorted CD4+CD25+suppressor T cellsand incubated in round bottom 96-well tissue culture plates with 0.5μg/ml of anti-CD3 antibody in 200 μl of CTL media. Forty-eight to 72hours later, cultures were pulsed with 1 μCi ³H-thymidine and incubatedan additional 16 hours before harvest with a Packard Micromate cellharvester. Determination of the amount of incorporated radioactivecounts was performed with a Packard Matrix 96 direct beta counter(Packard Biosciences, Meriden, Conn.).

Quantitative Real-Time PCR Analysis

The sorted 6.5 CD4+ T cells were immediately used for RNA extractionusing Trizol reagent (Invitrogen, Carlsbad, Calif.). Reversetranscription was performed with the Superscript First Strand SynthesisSystem (Invitrogen, Carlsbad, Calif.). cDNA levels were analyzed byreal-time quantitative PCR with the Taqman system (Applied Biosystems,Foster City, Calif.). Each sample was assayed in duplicates ortriplicates for the target gene together with 18S rRNA as the internalreference in 25 μl final reaction volume, using the Taqman Universal PCRMaster Mix and the ABI Prism 7700 Sequence Detection system. Pre-madereaction reagents (PDARs) were purchased from Applied Biosystems fordetection of IL-10 and IL-2. Primer pair and probe sets were designedusing Primer Express software and then synthesized by Applied Biosystemsfor LAG-3, CD25, GITR and IFN-γ. Primer and probe set used for Foxp3 wasquoted from literature (S4). The relative mRNA frequencies weredetermined by normalization to the internal control 18S RNA. Briefly, wenormalized each set of samples using the difference in the thresholdcycles (Ct) between the target gene and the 18S RNA:ΔCt_(sample)=(Ct_(sample)−Ct_(18S)). The calibration sample was assignedas the sample with the highest ΔCt in each set of assay(ΔCt_(calibration)). Relative mRNA frequencies were calculated as2^(ΔΔCt) where ΔCt=(ΔCt_(calibration)−ΔCt_(sample)). Primers and probesets used are: LAG-3 Primer 5′-ACA TCA ACC AGA CAG TGG CCA-3′ (SEQ IDNO: 9)/Primer 5′-GCA TCC CCT GGT GAA GGT C-3′ (SEQ ID NO: 10)/Probe5′-6FAM-CCC ACT CCC ATC CCG GCC C-TAMRA-3′ (SEQ ID NO: 11); CD25 Primer5′-TGT ATG ACC CAC CCG AGG TC-3′ (SEQ ID NO: 12)/Primer 5′-TTA GGA TGGTGC CGT TCT TGT-3′ (SEQ ID NO: 13)/Probe 5′-6FAM-CCA ATG CCA CAT TCA AAGCCC TCT CC-TAMRA-3′ (SEQ ID NO: 14); GITR Primer 5′-TCC GGT GTG TTG CCTGTG-3′ (SEQ ID NO: 15)/Primer 5′-CAA AGT CTG CAG TGA CCG TCA-3′ (SEQ IDNO: 16)/Probe 5′-6FAM-CAT GGG CAC CTT CTC CGC AGG T-TAMRA-3′ (SEQ ID NO:17); IFN-γ Primer 5′-CAT TGA AAG CCT AGA AAG TCT GAA TAA C-3′ (SEQ IDNO: 18)/Primer 5′-TGG CTC TGC AGG ATT TTC ATG-3′ (SEQ ID NO: 19)/Probe5′-6FAM-TCA CCA TCC TTT TGC CAG TTC CTC CAG-TAMRA-3′ (SEQ ID NO: 20);Foxp3 Prime 5′-CCC AGG AAA GAC AGC AAC CTT-3′ (SEQ ID NO: 21)/Primer5′-TTC TCA CAA CCA GGC CAC TTG-3′ (SEQ ID NO: 22)/Probe: 5′-6FAM-ATC CTACCC ACT GCT GGC AAA TGG AGT C-3′ (SEQ ID NO: 23).

LAG-3 Constructs and Retroviral Producer Cell Lines.

LAG-3 constructs were produced using recombinant PCR as described(Vignali and Vignali, 1999). The LAG-3.WT and the functionally nullmutant LAG-3.Y73F.ΔCY (cytoplasmic tailless LAG-3 with a point mutationthat greatly reduces the ability of LAG-3 to bind MHC class II) havebeen described (Workman et al., 2002a). LAG-3 constructs were clonedinto a murine stem cell virus (MSCV)-based retroviral vector, whichcontained an internal ribosomal entry site (IRES) and green fluorescentprotein (GFP), and retrovirus was produced as described (Persons et al.,1997; Persons et al., 1998). Retroviral producer cell lines weregenerated by repeatedly transducing GPE+86 cells (˜7-10 times) until aviral titer of greater than 10⁵/ml after 24 h was obtained (Markowitz etal., 1988).

Retroviral Transduction of CD4+/CD25− T Cells and In Vitro SuppressionAssay.

Splenocytes from 6.5 mice were stained with biotin labeled anti-B220,anti-Gr1, anti-Mac1, anti-TER119, anti-CD49b, anti-CD8 and anti-CD25antibody (PharMingen, San Diego, Calif.). The cells were then incubatedwith magnetic beads coupled with streptavidin and negatively sorted onan autoMACS (Miltenyi Biotech, Auburn Calif.) to 90-95% purity ofCD4⁺/CD25⁻ T cells. The purified 6.5 CD4⁺/CD25⁻ T cells were activatedby plate bound anti-CD3 (2C11) and anti-CD28 (35.71). On days 2 and 3post-stimulation, the activated T cells (4×10⁵ cells/ml) were spintransduced (90 min, 3000 rpm) with viral supernatant from vector alone,LAG-3.WT/GFP or LAG-3.Y73F.ΔCY/GFP retroviral GPE+86 producer cell linesdescribed above plus IL-2 and polybrene (6 μg/ml). The cells wereallowed to rest for 10 days and then sorted on the top ˜30-35%GFP⁺/Thy1.2⁺ T cells.

For the in vitro suppression assay, the purified GFP⁺ T cells werecultured (2 fold dilutions starting at 2.5×10⁴) with 2.5×10⁴ CD4⁺/CD25⁻6.5 T cells (purified by negative AutoMACS), 5×10⁴ irradiated (3000rads) splenocytes, and 5 μg/ml HA110120 in a 96-well round bottom plate.The cells were cultured for 72 h and pulsed with [³H]thymidine 1μCi/well (Du Pont, Wilmington, Del.) the last 7-8 h of culture.

Example 11

CD223 is cleaved from the cell surface and released in a soluble form(sLAG-3). It is generated in significant amounts by activated T cells invitro (5 μg/ml) and is also found in the serum of mice (80 ng/ml). It islikely generated by a cell surface protease. We detected sLAG-3 byWestern blot. The cleavage occurs in the transmembrane region (e.g.,amino acids 442-466 in SEQ ID NO: 2) or in the connector region (e.g.,amino acids 432-441 in SEQ ID NO: 2) immediately preceding itamino-terminally.

Example 12

As shown above, LAG-3 is not only required for maximal regulatory Tcells (Treg) function but is also sufficient. In other words, expressionof LAG-3 alone is sufficient to convert cells from activated effector Tcells into regulatory T cells.

We next wanted to determine if cells ectopically expressing LAG-3 wouldalso exhibit regulatory function in vivo and be protected in a diseasesetting. We chose to ask whether ectopic expression of LAG-3 on anautoantigen-specific T cell could protect mice from type 1 diabetes. Inthis experimental system, splenocytes from diabetes-prone NOD mice wereadoptively transferred to NOD-Scid mice, which lack lymphocytes. Allmice develop diabetes within 3 months. Our preliminary analysis suggeststhat diabetes onset induced by NOD splenocytes is prevented byphogrin-specific T cells transduced with LAG-3, but not a signalingdefective mutant or the GFP control. These data support the idea ofusing ectopic expression of auto-antigen specific T cells with LAG-3 asa novel therapeutic for the treatment of many autoimmune diseases,asthma, and allergy.

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1. A method of treating a patient suffering from an autoimmune disease, comprising: transfecting in vitro auto-immune T cells isolated from the patient with an expression construct comprising a coding sequence for CD223; reinfusing the transfected auto-immune T cells to the patient.
 2. The method of claim 1 wherein the patient suffers from multiple sclerosis.
 3. A composition, comprising: antibodies which specifically bind to CD223; and an anti-cancer vaccine.
 4. The composition of claim 3 which is a pharmaceutical composition.
 5. The composition of claim 3 wherein the antibodies are monoclonal antibodies.
 6. The composition of claim 3 wherein the composition is formed in vivo after administration to a patient.
 7. A kit comprising: antibodies which specifically bind to CD223; and an anti-cancer vaccine.
 8. The kit of claim 7 wherein said antibodies and vaccine are in separate containers.
 9. The kit of claim 7 further comprising instructions for administration of components of the kit to a cancer patient.
 10. An improved method of treating a cancer patient with an anti-cancer vaccine, comprising: administering to the cancer patient an antibody which specifically binds to CD223; administering to the cancer patient an anti-cancer vaccine, wherein the antibody increases magnitude of anti-cancer response of the cancer patient to the anti-cancer vaccine.
 11. A method to overcome suppression of an immune response to an anti-cancer vaccine, comprising: administering an antibody which specifically binds to CD223 to a cancer patient with regulatory T-cells which suppress an immune response to an anti-cancer vaccine; administering to the cancer patient an anti-cancer vaccine, whereby the antibody increases the response of the cancer patient to the anti-cancer vaccine.
 12. The method of claim 11 wherein the antibody is monoclonal.
 13. A method for increasing number of T cells in a mammal, comprising: administering to the mammal an inhibitory agent which binds to CD223 protein or CD223 mRNA.
 14. The method of claim 13 wherein the inhibitory agent is an antibody which specifically binds to CD223 protein.
 15. The method of claim 13 wherein the inhibitory agent is an antisense construct which expresses an antisense RNA molecule which is complementary to at least 7 nucleotides of CD223 mRNA.
 16. The method of claim 13 wherein the inhibitory agent is an antisense oligonucleotide which is complementary to at least 7 nucleotides of CD223 mRNA.
 17. The method of claim 13 wherein the inhibitory agent is a ribozyme which specifically binds to CD223 mRNA.
 18. The method of claim 13 wherein the inhibitory agent is an RNA interference molecule which specifically binds to CD223 mRNA.
 19. The method of claim 13 wherein the mammal is a cancer patient.
 20. The method of claim 13 wherein the mammal is bone marrow transplantation recipient.
 21. The method of claim 19 further comprising the step of vaccinating the cancer patient with anti-tumor vaccine.
 22. The method of claim 19 further comprising the step of transferring a tumor-specific T cell population to the cancer patient.
 23. The method of claim 19 further comprising the step of administering an anti-cancer chemotherapeutic drug to the patient.
 24. The method of claim 19 further comprising the step of administering anti-cancer antibodies to the patient.
 25. The method of claim 13 wherein the mammal has a chronic viral infection.
 26. The method of claim 25 further comprising the step of administering an anti-viral vaccine to the mammal.
 27. The method of claim 13 wherein the mammal has a chronic bacterial infection.
 28. The method of claim 27 further comprising the step of administering an anti-bacterial vaccine to the mammal.
 29. The method of claim 25 wherein the chronic viral infection is HIV.
 30. A method for increasing number of T cells in a population of T cells, comprising: administering to a population of T cells in vitro an inhibitory agent which binds to CD223 protein or CD223 mRNA.
 31. The method of claim 30 wherein the inhibitory agent is an antibody which specifically binds to CD223 protein.
 32. The method of claim 30 wherein the inhibitory agent is an antisense construct which expresses an antisense RNA molecule which is complementary to at least 7 nucleotides of CD223 mRNA.
 33. The method of claim 30 wherein the inhibitory agent is an antisense oligonucleotide which is complementary to at least 7 nucleotides of CD223 mRNA.
 34. The method of claim 30 wherein the inhibitory agent is a ribozyme which specifically binds to CD223 mRNA.
 35. The method of claim 30 wherein the inhibitory agent is an RNA interference molecule which specifically binds to CD223 mRNA.
 36. A method for decreasing number of T cells in a mammal, comprising: administering to the mammal an expression construct which encodes CD223, whereby CD223 is expressed from the expression construct and concentration of CD223 in the mammal is increased, and the number of T cells in the mammal is decreased.
 37. The method of claim 36 wherein the mammal is an autoimmune disease patient.
 38. A method for decreasing number of T cells in a mammal, comprising: administering to the mammal a population of CD223+T cells, whereby the concentration of CD223 in the mammal is increased and the number of T cells in the mammal is decreased.
 39. The method of claim 38 wherein the mammal is an autoimmune disease patient.
 40. The method of claim 39 wherein the CD223⁺ T cells are CD4⁺ T cells which have been transduced with an expression construct which encodes CD223.
 41. The method of claim 39 wherein the CD223⁺ T cells are auto-antigen specific T cells which have been transduced with an expression construct which encodes CD223.
 42. A polypeptide consisting of 50 or less contiguous amino acid residues of CD223, wherein the polypeptide comprises an amino acid sequence KIEELE as shown in SEQ ID NO:
 5. 43. A fusion polypeptide which comprises at least two segments, wherein a first segment consists of 50 or less contiguous amino acid residues of CD223, wherein the first segment comprises an amino acid sequence KIELLE as shown in SEQ ID NO: 5, wherein a second segment comprises an amino acid sequence which is not found in CD223 as shown in SEQ ID NO: 2 or
 4. 44. A method of testing substances for potential activity as a drug for treating cancer, autoimmune disease, chronic infections, AIDS, bone marrow transplantation recipients, comprising: contacting a test substance with a CD223 protein or CD223 protein fragment comprising an amino acid sequence KIELLE as shown in SEQ ID NO: 5; determining whether the test substance bound to the CD223 protein or CD223 protein fragment; identifying the test substance as a potential drug for treating cancer, autoirmmune disease, chronic infections, AIDS, or bone marrow transplantation recipients if the test substance bound to the CD223 protein or CD223 protein fragment.
 45. A method of testing substances for potential activity as a drug for treating cancer, chronic infections, AIDS, and bone marrow transplantation recipients, comprising: contacting a test substance with a CD223 protein; determining CD223 activity in the presence and absence of the test substance; identifying a test substance as a potential drug for treating cancer, chronic infections, AIDS, and bone marrow transplantation recipients if the test substance inhibits the CD223 activity.
 46. A method of testing substances for potential activity as a drug for treating autoimmune disease, comprising: contacting a test substance with a CD223 protein; determining CD223 activity in the presence and absence of the test substance; identifying a test substance as a potential drug for treating autoimmune disease if the test substance increases the CD223 activity.
 47. A method of testing substances for potential activity as a drug for treating cancer, chronic infections, AIDS, and bone marrow transplantation recipients, comprising: contacting a CD223⁺ T cell with a test substance; determining CD223 expression in the cell in the presence and absence of the test substance; identifying a test substance as a potential drug for treating cancer, chronic infections, AIDS, and bone marrow transplantation recipients if the test substance inhibits the CD223 expression in the T cell.
 48. A method of testing substances for potential activity as a drug for treating autoimmune disease, comprising: contacting a test substance with a CD223⁺ T cell; determining CD223 expression in the cell in the presence and absence of the test substance; identifying a test substance as a potential drug for treating autoimmune disease if the test substance increases the CD223 expression in the T cell.
 49. A method of isolating CD223⁺ T cells or CD223⁻ T cells, comprising: contacting a mixed population of T cells with an antibody which specifically binds to CD223 according to SEQ ID NO: 2 or 4; separating T cells which are bound to the antibody from T cells which are not bound to the antibody, thereby forming a population of CD223⁺ T cells and a population of CD223⁻ T cells.
 50. The method of claim 49 further comprising the step of transferring the population of CD223⁺ T cells to an autoimmune disease patient.
 51. The method of claim 49 wherein prior to the step of transferring the population to an autoimmune disease patient, the population is activated in vitro with an auto-antigen.
 52. The method of claim 49 wherein the mixed population of T cells is a sample of donor lymphocytes.
 53. The method of claim 52 further comprising the step of transferring the population of CD223⁻ T cells to a cancer patient.
 54. The method of claim 49 wherein the mixed population of T cells is tumor-specific.
 55. The method of claim 54 further comprising the step of transferring the population of CD223⁻ T cells to a cancer patient.
 56. An isolated soluble murine CD223 protein comprising residues 1 to 431 and lacking residues 467 to
 521. 57. The isolated soluble CD223 protein of claim 56 which is produced by a protease on the surface of CD223⁺ T cells.
 58. The isolated soluble CD223 protein of claim 56 which is free of other serum proteins.
 59. An isolated soluble human CD223 protein comprising residues 1 to 440 and lacking residues 475 to
 525. 60. The isolated soluble CD223 protein of claim 59 which is produced by a protease on the surface of CD223⁺ T cells.
 61. The isolated soluble CD223 protein of claim 59 which is free of other serum proteins.
 62. A method for decreasing number of T cells in a mammal, comprising: administering to the mammal a soluble CD223 protein whereby MHC class II-restricted/CD4+ T cell responses in the mammal are modulated.
 63. The method of claim 62 wherein the mammal is an autoimmune disease patient.
 64. The method of claim 62 wherein the mammal is an allergy patient.
 65. The method of claim 62 wherein the mammal is an asthma patient. 